Research shaders for compositor ops

AGENTS.md

@@ -234,7 +234,7 @@ WpAllocator scratch = wpMemArenaAllocatorInitZero(KiB(16));
 
 ## Documentation
 
-Save research notes and implementation plans as markdown in `documents/`:
+Save research notes, implementation plans and session logs as markdown in `documents/`:
 
 ```
 documents/
@@ -248,6 +248,9 @@ documents/
     └── YYYY-MM-DD.md
 ```
 
+At the start of each new session, read the previous session logs to understand what
+we've implemented so far
+
 ## Skills
 
 Domain-specific conventions are stored as skills in `.opencode/skills/<name>/SKILL.md`.

assets/blit.slang

@@ -0,0 +1,41 @@
+// Prism fullscreen texture blit shader.
+//
+// Draws a selected texture from the bindless array as a fullscreen quad that
+// is letterboxed/pillarboxed to preserve aspect ratio (contain-fit). The NDC
+// content rect is supplied via push constants so the texture is never
+// stretched, squashed, or cropped.
+
+struct BlitData {
+	float4 rect;   // NDC fit rect: x0, y0, x1, y1
+	uint   selected;
+	uint   mode;   // 0 = sample texture, 1 = solid background
+	uint   pad[2];
+};
+
+[[vk::push_constant]]
+BlitData blit;
+
+Sampler2D textures[];
+
+struct VSOutput {
+	float4 Pos : SV_POSITION;
+	float2 UV;
+};
+
+[shader("vertex")]
+VSOutput main(uint vertexIndex : SV_VertexID) {
+	VSOutput output;
+	float2 uv = float2(float(vertexIndex & 1), float((vertexIndex >> 1) & 1));
+	output.UV = uv;
+	float2 pos = lerp(blit.rect.xy, blit.rect.zw, uv);
+	output.Pos = float4(pos, 0.0, 1.0);
+	return output;
+}
+
+[shader("fragment")]
+float4 main(VSOutput input) {
+	if (blit.mode == 1) {
+		return float4(0.18, 0.18, 0.18, 1.0);
+	}
+	return textures[NonUniformResourceIndex(blit.selected)].Sample(input.UV);
+}

assets/shader.slang

@@ -1,61 +0,0 @@
-/* Copyright (c) 2025-2026, Sascha Willems
- *
- * SPDX-License-Identifier: MIT
- *
- */
-
-struct VSInput {
-	float3 Pos;
-	float3 Normal;
-	float2 UV;
-};
-
-Sampler2D textures[];
-
-struct ShaderData {
-	float4x4 projection;
-	float4x4 view;
-	float4x4 model[3];
-	float4 lightPos;
-	uint32_t selected;
-};
-
-struct VSOutput {
-	float4 Pos : SV_POSITION;
-	float3 Normal;
-	float2 UV;
-	float3 Factor;
-	float3 LightVec;
-	float3 ViewVec;
-	uint32_t InstanceIndex;
-};
-
-[shader("vertex")]
-VSOutput main(VSInput input, uniform ShaderData *shaderData, uint instanceIndex : SV_VulkanInstanceID) {
-	VSOutput output;
-	float4x4 modelMat = shaderData->model[instanceIndex];
-	output.Normal = mul((float3x3)mul(shaderData->view, modelMat), input.Normal);
-	output.UV = input.UV;
-	output.Pos = mul(shaderData->projection, mul(shaderData->view, mul(modelMat, float4(input.Pos.xyz, 1.0))));
-	output.Factor = (shaderData->selected == instanceIndex ? 3.0f : 1.0f);
-	output.InstanceIndex = instanceIndex;
-	// Calculate view vectors required for lighting
-	float4 fragPos = mul(mul(shaderData->view, modelMat), float4(input.Pos.xyz, 1.0));
-	output.LightVec = shaderData->lightPos.xyz - fragPos.xyz;
-	output.ViewVec = -fragPos.xyz;
-	return output;
-}
-
-[shader("fragment")]
-float4 main(VSOutput input) {
-	// Phong lighting
-	float3 N = normalize(input.Normal);
-	float3 L = normalize(input.LightVec);
-	float3 V = normalize(input.ViewVec);
-	float3 R = reflect(-L, N);
-	float3 diffuse = max(dot(N, L), 0.0025);
-	float3 specular = pow(max(dot(R, V), 0.0), 16.0) * 0.75;
-	// Sample from texture
-	float3 color = textures[NonUniformResourceIndex(input.InstanceIndex)].Sample(input.UV).rgb * input.Factor;
-	return float4(diffuse * color.rgb + specular, 1.0);
-}

assets/suzanne.mtl

@@ -1,62 +0,0 @@
-# Blender 5.0.1 MTL File: 'suzanne4.blend'
-# www.blender.org
-
-newmtl Material
-Ns 250.000000
-Ka 1.000000 1.000000 1.000000
-Kd 0.800000 0.800000 0.800000
-Ks 0.500000 0.500000 0.500000
-Ke 0.000000 0.000000 0.000000
-Ni 1.500000
-d 1.000000
-illum 2
-
-newmtl Material.001
-Ns 250.000000
-Ka 1.000000 1.000000 1.000000
-Kd 0.127605 0.127605 0.127605
-Ks 0.500000 0.500000 0.500000
-Ke 0.000000 0.000000 0.000000
-Ni 1.500000
-d 1.000000
-illum 2
-
-newmtl Material.002
-Ns 250.000000
-Ka 1.000000 1.000000 1.000000
-Kd 0.000000 0.000000 0.000000
-Ks 0.500000 0.500000 0.500000
-Ke 0.000000 0.000000 0.000000
-Ni 1.500000
-d 1.000000
-illum 2
-
-newmtl Material.003
-Ns 250.000000
-Ka 1.000000 1.000000 1.000000
-Kd 0.800000 0.800000 0.800000
-Ks 0.500000 0.500000 0.500000
-Ke 0.000000 0.000000 0.000000
-Ni 1.500000
-d 1.000000
-illum 2
-
-newmtl Material.004
-Ns 250.000000
-Ka 1.000000 1.000000 1.000000
-Kd 0.800007 0.200800 0.327761
-Ks 0.500000 0.500000 0.500000
-Ke 0.000000 0.000000 0.000000
-Ni 1.500000
-d 1.000000
-illum 2
-
-newmtl Material.005
-Ns 250.000000
-Ka 1.000000 1.000000 1.000000
-Kd 1.000000 1.000000 1.000000
-Ks 0.500000 0.500000 0.500000
-Ke 0.000000 0.000000 0.000000
-Ni 1.500000
-d 1.000000
-illum 2

documents/plans/fullscreen-blit.md

@@ -0,0 +1,150 @@
+# Plan — Fullscreen Texture Blit with Contain-Fit
+
+## Goal
+
+Render a texture fullscreen with aspect-ratio preservation. If the texture's
+aspect ratio does not match the window's, draw it to fit within the window —
+never stretched, squashed, or cropped. Tall/narrow textures pillarbox (bars on
+left/right); wide textures letterbox (bars on top/bottom).
+
+This replaces the Suzanne mesh demo in `main.cpp`, which was for testing the RHI.
+
+## Fit semantics (contain — never crop)
+
+```
+scale       = min(win_w / tex_w, win_h / tex_h)
+content_w   = tex_w * scale
+content_h   = tex_h * scale
+rect        = centered: left = (win_w - content_w)/2, top = (win_h - content_h)/2
+```
+
+| Texture vs window aspect | Limiting dim | Result            |
+|--------------------------|--------------|-------------------|
+| equal                    | —            | fills exactly     |
+| wider (e.g. 2048x512)    | width        | letterbox (T/B)   |
+| taller (e.g. 512x2048)   | height       | pillarbox (L/R)   |
+
+The fit rect is recomputed per frame from the selected texture's dimensions and
+the current window size, so window resize works without extra handling.
+
+## Changes
+
+### 1. RHI — texture size accessor
+
+Add a value struct and a by-value getter (matches `prRhiGetSurfaceCapabilities`
+pattern):
+
+```c
+typedef struct PrRhiTextureSize {
+	u32 width;
+	u32 height;
+} PrRhiTextureSize;
+
+PrRhiTextureSize prRhiGetTextureSize(PrRhiTexture *texture);
+```
+
+Files: `pr_rhi_types.h`, `pr_rhi.h`, `vulkan/pr_rhi_vk.h`,
+`vulkan/pr_rhi_vk.c`, `vulkan/pr_rhi_vk_aliases.h`.
+
+### 2. Offline shader compilation (drop Slang runtime)
+
+- New `justfile` `shaders` recipe:
+  `slangc -target spirv -profile spirv_1_4 -o build/shaders/blit.spv assets/blit.slang`
+  (entry points auto-detected from `[shader(...)]` attributes).
+  `build` depends on it.
+- `main.cpp` loads `build/shaders/blit.spv` via wapp file I/O
+  (`wpFileOpen` / `wpFileGetLength` / `wpFileRead`) into an arena buffer, then
+  `prRhiCreateShader`. No `slang.h` includes, no runtime compilation.
+- Drop `-lslang` and the `-I .../slang` include from the build.
+
+### 3. `assets/blit.slang`
+
+Push constant block (32 bytes — Slang pads structs to 16-byte alignment, so the
+C++ struct carries explicit `pad[3]` to match):
+
+```hlsl
+struct BlitData {
+	float4 rect;   // NDC fit rect: x0, y0, x1, y1
+	uint   selected;
+	uint   pad[3];
+};
+```
+
+- **VS**: generates a 4-vertex triangle-strip quad from `SV_VertexID` (no vertex
+  buffer), maps UV 0–1 into the NDC rect.
+- **FS**: `textures[NonUniformResourceIndex(selected)].Sample(uv)` — reuses the
+  existing bindless descriptor array.
+
+### 4. `main.cpp` — clean texture viewer
+
+Remove everything mesh-related: tinyobj loading, vertex/index buffers,
+`ShaderData` storage buffers / device addresses, the mesh shader + pipeline,
+mouse orbit, and the mesh draw. Drop `-ltinyobjloader -lglm` from the link.
+Remove unused `assets/shader.slang`, `suzanne.obj`, `suzanne.mtl`.
+
+New flow: RHI init → window/instance/pdev/surface/device/swapchain → load 7
+textures → bindless descriptor set (variable count 7) → load `blit.spv` →
+blit pipeline layout (`VERTEX|FRAGMENT` 32-byte push range) → blit pipeline
+(no vertex input, `TRIANGLE_STRIP`, swapchain color format, no depth,
+`cull NONE`, dynamic viewport/scissor).
+
+Render loop per frame:
+- `compute_fit_rect()` from the selected texture's dims + window size
+- bind blit pipeline + descriptor set, push `BlitData{ rect, selected }`,
+  `prRhiCmdDraw(cb, 4, 1, 0, 0)`
+- `+/-` cycles the selected texture; resize recomputes fit automatically
+
+### 5. Test textures (PIL + `build/bin/toktx`)
+
+Four generated KTX files in `assets/`, loaded alongside the 3 Suzanne textures
+(`texture_count = 7`, explicit path array):
+
+| File            | Size      | Shows                    |
+|-----------------|-----------|--------------------------|
+| `test_square.ktx` | 1024x1024 | bars on both axes        |
+| `test_fill.ktx`   | 1920x1080 | fills the 16:9 window    |
+| `test_wide.ktx`   | 2048x512  | letterbox (T/B)          |
+| `test_tall.ktx`   | 512x2048  | pillarbox (L/R)          |
+
+Each with distinct gradients + a border grid so any stretch/squash is visible.
+Generated with `--genmipmap` for mip-aware sampling.
+
+## Verification
+
+`just build && just run` — each texture fits without crop/stretch, `+/-` cycles,
+window resize keeps fit, no Slang runtime in the binary.
+
+## Verification results (2026-08-08)
+
+Fit behavior confirmed by capturing the window (X11 driver) and sampling pixels:
+
+| Texture             | Window        | Result verified                                |
+|---------------------|---------------|------------------------------------------------|
+| square 1024x1024    | 16:9 wide     | pillarbox — pure-black L/R bars, full height   |
+| test_wide 2048x512  | 16:9 wide     | letterbox — pure-black T/B bars, full width    |
+| test_tall 512x2048  | 16:9 wide     | pillarbox — pure-black L/R bars, full height   |
+| test_fill 1920x1080 | 16:9 wide     | fills exactly — no bars anywhere               |
+| square (resized)    | portrait      | fit recomputed per frame — flips to letterbox  |
+
+Texture cycling (`+/-`, `SDLK_PLUS/KP_PLUS/EQUALS`, `SDLK_MINUS/KP_MINUS`) is a
+straightforward `selected` bump in the key handler; it was reviewed but not
+exercise-tested in the headless verification env (KWin/XWayland drops XTEST
+synthesised keys). The other fit cases were verified by temporarily launching
+each texture as the initial selection.
+
+### Bugs found and fixed during verification
+
+1. **`VK_SUBOPTIMAL_KHR` aborted the app.** `prRhiAcquireNextImageVk` /
+   `prRhiPresentVk` routed `SUBOPTIMAL` into `_checkVk` → `__builtin_trap()`.
+   Both now treat it like `OUT_OF_DATE` (return `PR_RHI_SWAPCHAIN_OUT_OF_DATE`).
+   Triggered immediately under X11/XWayland.
+2. **Swapchain recreate ignored surface extent.** `prRhiRecreateSwapchainVk`
+   hard-coded the passed width/height; on surfaces whose `currentExtent` is
+   meaningful (X11) that mismatched the drawable and re-looped on SUBOPTIMAL.
+   Now queries `vkGetPhysicalDeviceSurfaceCapabilitiesKHR` and falls back to the
+   passed size only when `currentExtent == 0xFFFFFFFF`.
+3. **App used logical window size for the swapchain.** Under HiDPI the drawable
+   differs from `SDL_GetWindowSize` (1920x1080 logical → 2400x1350 drawable at
+   1.25x scale), which is the root cause of #1 under XWayland. main.cpp now uses
+   `SDL_GetWindowSizeInPixels` for swapchain width/height, fit math, viewport
+   and scissor.

documents/session-logs/2026-08-08.md

@@ -0,0 +1,60 @@
+# Session Log — 2026-08-08
+
+## Fullscreen Texture Viewer — Verification and RHI Fixes
+
+Continuation of the fullscreen-blit plan (`documents/plans/fullscreen-blit.md`),
+which rewrote `main.cpp` from the Suzanne mesh demo into a bindless texture
+viewer with contain-fit. This session visually verified the renderer and fixed
+three real bugs uncovered by that verification.
+
+### Verification method
+
+- Ran the app under the X11 SDL driver (`SDL_VIDEODRIVER=x11`) and captured the
+  window with `xwd -id <window>`, then sampled pixels with ImageMagick
+  (`magick -format "%[pixel:p{x,y}]" info:`). The model cannot view images, so
+  all render checks were programmatic (pure-black bars, centered content).
+- XTEST synthesised keys (`XTestFakeKeyEvent`) are silently dropped by
+  KWin/XWayland (confirmed with `xev`: FocusIn arrives via `_NET_ACTIVE_WINDOW`,
+  KeyPress never does). So texture cycling could not be driven headlessly; fit
+  cases were verified by temporarily making each texture the initial selection.
+
+### Contain-fit verified (pixel-sampled)
+
+| Texture             | Window    | Result                                |
+|---------------------|-----------|---------------------------------------|
+| square 1024x1024    | 16:9      | pillarbox (black L/R bars)            |
+| test_wide 2048x512  | 16:9      | letterbox (black T/B bars)            |
+| test_tall 512x2048  | 16:9      | pillarbox (black L/R bars)            |
+| test_fill 1920x1080 | 16:9      | fills exactly (no bars)               |
+| square, then resized to portrait | portrait | fit recomputed per frame → flips to letterbox |
+
+### Bugs found and fixed
+
+1. **`VK_SUBOPTIMAL_KHR` crashed the app.** `prRhiAcquireNextImageVk` and
+   `prRhiPresentVk` routed SUBOPTIMAL into `_checkVk` → `__builtin_trap()`
+   (SIGILL, caught under X11 immediately). Both now return
+   `PR_RHI_SWAPCHAIN_OUT_OF_DATE` for SUBOPTIMAL, same as OUT_OF_DATE
+   (`pr_rhi_vk.c`).
+2. **Swapchain recreate ignored surface extent.** `prRhiRecreateSwapchainVk`
+   hard-coded the passed width/height. Now queries
+   `vkGetPhysicalDeviceSurfaceCapabilitiesKHR` and falls back to the passed
+   size only when `currentExtent == 0xFFFFFFFF` (matches the initial-create
+   logic).
+3. **App used logical window size for the swapchain.** Under HiDPI the drawable
+   differs from `SDL_GetWindowSize` (1920x1080 logical vs 2400x1350 drawable at
+   1.25x scale on XWayland) — the root cause of #1. main.cpp now uses
+   `SDL_GetWindowSizeInPixels` for swapchain width/height, the fit rect, the
+   viewport, and the scissor.
+
+### CLI arg considered and removed
+
+Added a `--texture N` startup arg to drive the verification, then removed it at
+the user's request (`main()` is back to no-args, `app.selected = 0`). If
+headless key injection is ever needed again, revisit (e.g. `ydotool`/`wtype` on
+Wayland, or a WM on a real X server).
+
+### Notes
+
+- `main.cpp` header comment, `<cstdlib>` include, and plan doc all updated to
+  reflect the removed arg.
+- Native Wayland run still clean after all fixes; `just build` passes.

documents/session-logs/2026-08-09.md

@@ -0,0 +1,59 @@
+# Session Log — 2026-08-09
+
+## Background colour change (blit shader)
+
+- User requested changing the letterbox/pillarbox background from black to neutral grey.
+- Initial attempt: changed the render pass clear color to `(0.5, 0.5, 0.5, 1.0)`. This
+  triggered the NVIDIA validation layer warning
+  `BestPractices-NVIDIA-ClearColor-NotCompressed` — SRGB fast clears only work
+  with 0.0 or 1.0 on NVIDIA tile-based GPUs.
+- Reverted the clear color and implemented the proper solution: draw a fullscreen
+  grey quad in the fragment shader before the texture quad. The render pass clear
+  stays at 0.0 (fast-compressed).
+- Added `mode` field to `BlitData` push constant. Mode 0 samples the texture, mode
+  1 outputs solid grey.
+- User noted that a branch in the shader is free (no warp divergence since `mode`
+  is uniform per draw call). Agreed — no need for a separate clear pipeline.
+- Changed grey from 0.5 to 0.18 (18% grey card, standard in photography/compositing).
+- Fixed a Slang compilation warning by updating the profile from `spirv_1_4` to
+  `spirv_1_6` and explicitly declaring the required capabilities.
+
+## Shader filter node research
+
+- User requested research on: Gaussian blur, CDL, Laplacian, Sobel, sharpen,
+  posterize, pixelize, Kuwahara.
+- Launched a research agent that produced `documents/research/shader-filters.md`
+  covering all filters with formulas, Slang pseudocode, parameter tables, and
+  performance notes.
+
+## Design decisions made during review
+
+1. **Colour space**: all intermediate textures are linear float
+   (`R16G16B16A16_SFLOAT`, `R32G32B32A32_SFLOAT` for Kuwahara tensor). sRGB images
+   are linearized once at load by the Read node. Final blit to sRGB swapchain
+   handles display encoding.
+
+2. **Alpha**: premultiplied everywhere by default. Explicit Unpremult/Premult
+   nodes for operations that need unpremultiplied values (Nuke model).
+
+3. **Edge handling**: per-node parameter, clamp-to-edge default, clamp-to-border
+   option. Affects sampler state, not shader branches.
+
+4. **Premult has no parameters**: removed the empty push constant struct.
+
+## Research document fixes
+
+- Fixed a contradictory sentence about push constant sizes and CDL block size.
+- Added Unpremult (§9) and Premult (§10) sections with full implementations.
+- Added `edge_mode` field to all 5 spatial filter push constant blocks (Gaussian,
+  Laplacian, Sobel, Sharpen, Kuwahara).
+- Restructured the implications section (§12) into open items vs resolved decisions.
+- Expanded all mathematics sections with plain-language explanations suitable for
+  someone without a strong math background.
+
+## Open items for next session
+
+- Begin implementing the actual shader nodes in Prism
+- Node system needs: per-pass resource signatures, scratch texture hooks, per-node
+  sampler choice, compile-time-bounded loop limits
+- Classic Kuwahara is the recommended first implementation (single pass)

justfile

@@ -13,7 +13,7 @@ VENDOR_INC := BUILDDIR + "/include"
 VENDOR_LIB := BUILDDIR + "/lib"
 
 VK_FLAGS := "-DPR_RHI_VULKAN -DVK_NO_PROTOTYPES -I" + VK_SDK + "/include -I" + VK_SDK + "/include/vma -I" + VENDOR_INC
-APP_INC  := "-I" + VK_SDK + "/include -I" + VK_SDK + "/include/vma -I" + VK_SDK + "/include/slang -I" + VENDOR_INC + " -Isrc"
+APP_INC  := "-I" + VK_SDK + "/include -I" + VK_SDK + "/include/vma -I" + VENDOR_INC + " -Isrc"
 
 # Build KTX from source
 vendor:
@@ -30,8 +30,22 @@ vendor:
 	cmake --build {{BUILDDIR}}/ktx --config Release
 	cmake --install {{BUILDDIR}}/ktx
 
+# Compile shaders from .slang to SPIR-V
+shaders:
+	mkdir -p {{BUILDDIR}}/shaders
+	{{VK_SDK}}/bin/slangc -target spirv \
+		-profile spirv_1_6+\
+			SPV_GOOGLE_user_type+\
+			spvFragmentFullyCoveredEXT+\
+			spvDerivativeControl+\
+			spvImageQuery+\
+			spvImageGatherExtended+\
+			spvSparseResidency+\
+			spvMinLod \
+		-o {{BUILDDIR}}/shaders/blit.spv assets/blit.slang
+
 # Build all objects, then link
-build: vendor
+build: vendor shaders
 	mkdir -p {{BUILDDIR}}/bin
 	bear -- {{CXX}} -g -c -Wno-nullability-completeness {{VK_FLAGS}} \
 		src/prism/rhi/vulkan/profiles/vulkan_profiles.cpp \
@@ -50,7 +64,7 @@ build: vendor
 	bear -a -- {{CXX}} -g {{VK_FLAGS}} \
 		-L{{VK_SDK}}/lib -L{{VENDOR_LIB}} \
 		build/*.o \
-		-lSDL3 -lglm -ltinyobjloader -lktx -lslang -lvulkan \
+		-lSDL3 -lktx -lvulkan \
 		-Wl,-rpath,{{VENDOR_LIB}} -Wl,-rpath,{{VK_SDK}}/lib \
 		-o {{BUILDDIR}}/bin/prism
 	@echo "--- build done: {{BUILDDIR}}/bin/prism ---"

src/main.cpp

@@ -1,26 +1,18 @@
 // vim:fileencoding=utf-8:foldmethod=marker
 //
-// Prism port of how-to-vulkan's main.cpp — uses the RHI API instead of
-// direct Vulkan calls.
+// Prism texture viewer — draws a texture fullscreen with contain-fit
+// (letterbox/pillarbox to preserve aspect ratio, never crops or stretches).
+// Texture selection cycles with +/-.
 
 #include "prism/rhi/pr_rhi_types.h"
 #include "prism/rhi/pr_rhi.h"
 #include <SDL3/SDL_timer.h>
-#include <glm/ext/matrix_clip_space.hpp>
-#include <glm/glm.hpp>
-#include <glm/gtc/matrix_transform.hpp>
-#include <glm/gtc/quaternion.hpp>
 #include <SDL3/SDL.h>
 #include <SDL3/SDL_events.h>
 #include <SDL3/SDL_init.h>
 #include <SDL3/SDL_keycode.h>
 #include <SDL3/SDL_video.h>
-#include <slang/slang.h>
-#include <slang/slang-com-ptr.h>
-#include <tiny_obj_loader.h>
 #include <iostream>
-#include <vector>
-#include <cstdint>
 
 // ============================================================================
 // Exit codes
@@ -29,18 +21,12 @@
 enum ExitCode {
 	EXIT_CODE_SUCCESS,
 	EXIT_CODE_SDL_INIT_FAILED,
-	EXIT_CODE_VULKAN_LIB_LOAD_FAILED,
 	EXIT_CODE_WINDOW_CREATION_FAILED,
-	EXIT_CODE_SURFACE_CREATION_FAILED,
 	EXIT_CODE_GET_WINDOW_SIZE_FAILED,
-	EXIT_CODE_NO_INSTANCE_SUPPORT,
 	EXIT_CODE_NO_PHYSICAL_DEVICES,
-	EXIT_CODE_ALLOCATION_FAILURE,
 	EXIT_CODE_NO_SUITABLE_PHYSICAL_DEVICE,
-	EXIT_CODE_NO_PRESENTATION_SUPPORT,
-	EXIT_CODE_NO_SUITABLE_DEPTH_FORMAT,
-	EXIT_CODE_MESH_LOAD_FAILED,
-	EXIT_CODE_SYNC_OBJ_CREATE_FAILED,
+	EXIT_CODE_ALLOCATION_FAILURE,
+	EXIT_CODE_SHADER_LOAD_FAILED,
 };
 
 static inline void check(bool result, i32 code) {
@@ -54,39 +40,40 @@ static inline void check(bool result, i32 code) {
 // Types
 // ============================================================================
 
-struct Vertex {
-	glm::vec3 pos;
-	glm::vec3 normal;
-	glm::vec2 uv;
-};
-
-struct ShaderData {
-	glm::mat4 projection;
-	glm::mat4 view;
-	glm::mat4 model[3];
-	glm::vec4 light_pos{ 0.0f, -10.0f, 10.0f, 0.0f };
-	u32 selected{ 1 };
-};
-
 struct TextureResources {
 	PrRhiTexture *texture;
 	PrRhiSampler *sampler;
 };
 
+// Push constant block — matches BlitData in assets/blit.slang (16-byte aligned,
+// so the struct is padded to 32 bytes).
+struct BlitData {
+	f32 rect[4];   // NDC fit rect: x0, y0, x1, y1
+	u32 selected;
+	u32 mode;      // 0 = sample texture, 1 = solid background
+	u32 pad[2];
+};
+
 // Typedefs for wapp arrays of our types
-typedef Vertex             *VertexArray;
-typedef u16                *U16Array;
-typedef glm::vec3          *GlmVec3Array;
-typedef TextureResources   *TextureResourcesArray;
-typedef PrRhiBuffer        **PrRhiBufferArray;
-typedef PrRhiFence         **PrRhiFenceArray;
-typedef PrRhiSemaphore     **PrRhiSemaphoreArray;
-typedef PrRhiCommandBuffer **PrRhiCommandBufferArray;
+typedef TextureResources       *TextureResourcesArray;
+typedef PrRhiSemaphore        **PrRhiSemaphoreArray;
+typedef PrRhiFence            **PrRhiFenceArray;
+typedef PrRhiCommandBuffer    **PrRhiCommandBufferArray;
 
 // ============================================================================
 // Global state
 // ============================================================================
 
+static const char *const TEXTURE_PATHS[] = {
+	"assets/suzanne0.ktx",
+	"assets/suzanne1.ktx",
+	"assets/suzanne2.ktx",
+	"assets/test_square.ktx",
+	"assets/test_fill.ktx",
+	"assets/test_wide.ktx",
+	"assets/test_tall.ktx",
+};
+
 struct AppState {
 	PrRhiInstance       *inst;
 	PrRhiPhysicalDevice *pdev;
@@ -96,40 +83,62 @@ struct AppState {
 
 	PrRhiFormat swapchain_format;
 
-	PrRhiBuffer *vert_index_buf;
-	u64          vertex_buf_size;
-	u64          index_count;
-
 	static constexpr u32 max_frames_in_flight = 2;
-	static constexpr u32 instance_count       = 3;
-	static constexpr u32 texture_count        = 3;
+	static constexpr u32 texture_count        = (u32)(sizeof(TEXTURE_PATHS) / sizeof(TEXTURE_PATHS[0]));
 
-	PrRhiBufferArray           shader_data_bufs;
-	PrRhiFenceArray            fences;
-	PrRhiSemaphoreArray        image_acquired_semaphores;
-	PrRhiSemaphoreArray        render_completed_semaphores;
-	PrRhiCommandPool          *cmd_pool;
-	PrRhiCommandBufferArray    cmd_buffers;
+	PrRhiFenceArray          fences;
+	PrRhiSemaphoreArray      image_acquired_semaphores;
+	PrRhiSemaphoreArray      render_completed_semaphores;
+	u32                      render_semaphore_count;
+	PrRhiCommandPool        *cmd_pool;
+	PrRhiCommandBufferArray  cmd_buffers;
 
-	TextureResourcesArray      textures;
-	PrRhiDescriptorSetLayout  *desc_set_layout;
-	PrRhiDescriptorPool       *desc_pool;
-	PrRhiDescriptorSet        *desc_set;
+	TextureResourcesArray    textures;
+	PrRhiDescriptorSetLayout *desc_set_layout;
+	PrRhiDescriptorPool      *desc_pool;
+	PrRhiDescriptorSet       *desc_set;
 
-	PrRhiShader               *shader;
-	PrRhiPipelineLayout       *pipeline_layout;
-	PrRhiPipeline             *pipeline;
+	PrRhiShader             *shader;
+	PrRhiPipelineLayout     *pipeline_layout;
+	PrRhiPipeline           *pipeline;
 
-	ShaderData                 shader_data;
-	u32                        frame_index;
-	glm::ivec2                 window_size;
-	GlmVec3Array               object_rotations;
-	bool                       update_swapchain;
+	u32                      selected;
+	u32                      frame_index;
+	i32                      window_width;
+	i32                      window_height;
+	bool                     update_swapchain;
 
-	SDL_Window                *window;
-	Slang::ComPtr<slang::IGlobalSession> slang_session;
+	SDL_Window              *window;
 };
 
+// ============================================================================
+// Helpers
+// ============================================================================
+
+// Fills rect with the NDC bounds (x0, y0, x1, y1) of the texture content when
+// contained within the window, preserving aspect ratio and centering.
+static void computeFitRect(f32 tex_w, f32 tex_h, f32 win_w, f32 win_h, f32 *rect) {
+	if (win_w <= 0.0f || win_h <= 0.0f || tex_w <= 0.0f || tex_h <= 0.0f) {
+		rect[0] = -1.0f;
+		rect[1] = -1.0f;
+		rect[2] =  1.0f;
+		rect[3] =  1.0f;
+		return;
+	}
+
+	f32 scale_x = win_w / tex_w;
+	f32 scale_y = win_h / tex_h;
+	f32 scale   = scale_x < scale_y ? scale_x : scale_y;
+
+	f32 content_w = tex_w * scale;
+	f32 content_h = tex_h * scale;
+
+	rect[0] = -content_w / win_w;
+	rect[1] = -content_h / win_h;
+	rect[2] =  content_w / win_w;
+	rect[3] =  content_h / win_h;
+}
+
 // ============================================================================
 // Main
 // ============================================================================
@@ -144,7 +153,7 @@ int main() {
 	check(SDL_Init(SDL_INIT_VIDEO), EXIT_CODE_SDL_INIT_FAILED);
 
 	f32 display_scale = SDL_GetDisplayContentScale(SDL_GetPrimaryDisplay());
-	app.window        = SDL_CreateWindow("How To Vulkan (Prism)", (i32)(display_scale * 1920),
+	app.window        = SDL_CreateWindow("Prism — Texture Viewer", (i32)(display_scale * 1920),
 	                                     (i32)(display_scale * 1080),
 	                                     SDL_WINDOW_VULKAN | SDL_WINDOW_RESIZABLE);
 	check(app.window != nullptr, EXIT_CODE_WINDOW_CREATION_FAILED);
@@ -185,7 +194,7 @@ int main() {
 	// }}}
 
 	// {{{ Surface creation
-	check(SDL_GetWindowSize(app.window, &app.window_size.x, &app.window_size.y),
+	check(SDL_GetWindowSizeInPixels(app.window, &app.window_width, &app.window_height),
 	      EXIT_CODE_GET_WINDOW_SIZE_FAILED);
 	app.surface = prRhiCreateSurfaceFromWindow(app.inst, app.window);
 	// }}}
@@ -200,8 +209,8 @@ int main() {
 	// {{{ Swapchain creation
 	PrRhiSwapchainDesc swap_desc = {};
 	swap_desc.surface            = app.surface;
-	swap_desc.width              = (u32)app.window_size.x;
-	swap_desc.height             = (u32)app.window_size.y;
+	swap_desc.width              = (u32)app.window_width;
+	swap_desc.height             = (u32)app.window_height;
 	swap_desc.has_depth          = true;
 	swap_desc.depth_format       = PR_RHI_FORMAT_D24_UNORM_S8_UINT;
 
@@ -209,77 +218,7 @@ int main() {
 	app.swapchain_format = prRhiGetSwapchainFormat(app.swapchain);
 	// }}}
 
-	// {{{ Vertex/Index buffers
-	// {{{ Load mesh
-	tinyobj::attrib_t attrib;
-	std::vector<tinyobj::shape_t> shapes;
-	std::vector<tinyobj::material_t> materials;
-
-	check(tinyobj::LoadObj(&attrib, &shapes, &materials, nullptr, nullptr, "assets/suzanne.obj"),
-	      EXIT_CODE_MESH_LOAD_FAILED);
-
-	VertexArray vertices = wpArrayAllocCapacity(Vertex, &arena, 128, WP_ARRAY_INIT_NONE);
-	U16Array indices     = wpArrayAllocCapacity(u16, &arena, 128, WP_ARRAY_INIT_NONE);
-
-	for (auto &idx : shapes[0].mesh.indices) {
-		Vertex v = {};
-		v.pos    = {
-			 attrib.vertices[idx.vertex_index * 3],
-			-attrib.vertices[idx.vertex_index * 3 + 1],
-			 attrib.vertices[idx.vertex_index * 3 + 2]
-		};
-		v.normal = {
-			attrib.normals[idx.normal_index * 3],
-			-attrib.normals[idx.normal_index * 3 + 1],
-			attrib.normals[idx.normal_index * 3 + 2]
-		};
-		v.uv     = {
-			attrib.texcoords[idx.texcoord_index * 2],
-			1.0f - attrib.texcoords[idx.texcoord_index * 2 + 1]
-		};
-
-		u16 index = (u16)wpArrayCount(indices);
-		vertices  = wpArrayAppendAlloc(Vertex, &arena, vertices, &v, WP_ARRAY_INIT_NONE);
-		indices   = wpArrayAppendAlloc(u16, &arena, indices, &index, WP_ARRAY_INIT_NONE);
-	}
-
-	app.vertex_buf_size = sizeof(Vertex) * wpArrayCount(vertices);
-	app.index_count     = wpArrayCount(indices);
-	u64 index_buf_size  = sizeof(u16) * app.index_count;
-	// }}}
-
-	// {{{ Create GPU buffer
-	PrRhiBufferDesc vert_desc = {};
-	vert_desc.size            = app.vertex_buf_size + index_buf_size;
-	vert_desc.usage           = (PrRhiBufferUsage)(PR_RHI_BUFFER_USAGE_VERTEX | PR_RHI_BUFFER_USAGE_INDEX);
-	vert_desc.memory          = PR_RHI_MEMORY_CPU_TO_GPU;
-
-	app.vert_index_buf = prRhiCreateBuffer(app.device, vert_desc);
-
-	void *mapped = prRhiBufferMap(app.device, app.vert_index_buf);
-	memcpy(mapped, vertices, app.vertex_buf_size);
-	memcpy((u8 *)mapped + app.vertex_buf_size, indices, index_buf_size);
-	prRhiBufferUnmap(app.device, app.vert_index_buf);
-	// }}}
-	// }}}
-
-	// {{{ Shader data buffers
-	app.shader_data_bufs = wpArrayAllocCapacity(PrRhiBuffer *, &arena,
-	                                            AppState::max_frames_in_flight,
-	                                            WP_ARRAY_INIT_FILLED);
-	for (u32 i = 0; i < AppState::max_frames_in_flight; ++i) {
-		PrRhiBufferDesc buf_desc = {};
-		buf_desc.size            = sizeof(ShaderData);
-		buf_desc.usage           = (PrRhiBufferUsage)(PR_RHI_BUFFER_USAGE_STORAGE |
-		                                              PR_RHI_BUFFER_USAGE_SHADER_DEVICE_ADDRESS);
-		buf_desc.memory          = PR_RHI_MEMORY_CPU_TO_GPU;
-
-		app.shader_data_bufs[i] = prRhiCreateBuffer(app.device, buf_desc);
-	}
-	// }}}
-
 	// {{{ Synchronisation objects
-	// Fences
 	app.fences = wpArrayAllocCapacity(PrRhiFence *, &arena, AppState::max_frames_in_flight,
 	                                  WP_ARRAY_INIT_FILLED);
 	for (u32 i = 0; i < AppState::max_frames_in_flight; ++i) {
@@ -288,7 +227,6 @@ int main() {
 		app.fences[i] = prRhiCreateFence(app.device, fd);
 	}
 
-	// Image acquired semaphores (per frame)
 	app.image_acquired_semaphores = wpArrayAllocCapacity(PrRhiSemaphore *, &arena,
 	                                                     AppState::max_frames_in_flight,
 	                                                     WP_ARRAY_INIT_FILLED);
@@ -296,12 +234,11 @@ int main() {
 		app.image_acquired_semaphores[i] = prRhiCreateSemaphore(app.device);
 	}
 
-	// Render completed semaphores (per swapchain image)
-	u32 swapchain_image_count       = prRhiGetSwapchainImageCount(app.swapchain);
+	app.render_semaphore_count   = prRhiGetSwapchainImageCount(app.swapchain);
 	app.render_completed_semaphores = wpArrayAllocCapacity(PrRhiSemaphore *, &arena,
-	                                                       swapchain_image_count,
+	                                                       app.render_semaphore_count,
 	                                                       WP_ARRAY_INIT_FILLED);
-	for (u32 i = 0; i < swapchain_image_count; ++i) {
+	for (u32 i = 0; i < app.render_semaphore_count; ++i) {
 		app.render_completed_semaphores[i] = prRhiCreateSemaphore(app.device);
 	}
 	// }}}
@@ -320,11 +257,8 @@ int main() {
 	PrRhiCommandBuffer *upload_cb      = upload_cbs[0];
 
 	for (u32 i = 0; i < AppState::texture_count; ++i) {
-		char buf[2048] = {};
-		snprintf(buf, sizeof(buf), "assets/suzanne%u.ktx", i);
-		PrRhiTexture *tex = prRhiCreateTextureFromKtx(app.device, buf, app.cmd_pool, upload_cb);
+		PrRhiTexture *tex = prRhiCreateTextureFromKtx(app.device, TEXTURE_PATHS[i], app.cmd_pool, upload_cb);
 
-		// Create sampler
 		PrRhiSamplerDesc samp_desc = {};
 		samp_desc.mag_filter       = PR_RHI_FILTER_LINEAR;
 		samp_desc.min_filter       = PR_RHI_FILTER_LINEAR;
@@ -355,7 +289,6 @@ int main() {
 	PrRhiDescriptorSetLayoutDesc layout_desc = { ds_layouts };
 	app.desc_set_layout                      = prRhiCreateDescriptorSetLayout(app.device, layout_desc);
 
-	// Pool
 	PrRhiDescriptorPoolSize pool_size = {};
 	pool_size.type                    = PR_RHI_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER;
 	pool_size.descriptor_count        = AppState::texture_count;
@@ -366,12 +299,10 @@ int main() {
 
 	app.desc_pool = prRhiCreateDescriptorPool(app.device, ds_pool_desc);
 
-	// Allocate descriptor set (variable count)
 	WpU32Array var_counts = wpArray(u32, AppState::texture_count);
 	app.desc_set          = prRhiAllocateDescriptorSet(app.device, app.desc_pool, app.desc_set_layout,
 	                                                   var_counts);
 
-	// Write descriptor set
 	PrRhiDescriptorImageInfoArray img_infos = wpArrayAllocCapacity(PrRhiDescriptorImageInfo,
 	                                                               &arena,
 	                                                               AppState::texture_count,
@@ -394,39 +325,29 @@ int main() {
 	prRhiUpdateDescriptorSet(app.device, writes);
 	// }}}
 
-	// {{{ Shader compilation (Slang)
-	slang::createGlobalSession(app.slang_session.writeRef());
+	// {{{ Load blit shader (pre-compiled SPIR-V)
+	WpStr8RO spirv_path = wpStr8LitRo("build/shaders/blit.spv");
+	WpFile *spirv_file  = wpFileOpen(&arena, &spirv_path, WP_ACCESS_READ);
+	check(spirv_file != nullptr, EXIT_CODE_SHADER_LOAD_FAILED);
 
-	slang::TargetDesc target = {};
-	target.format  = SLANG_SPIRV;
-	target.profile = {app.slang_session->findProfile("spirv_1_4")};
+	i64 spirv_len = wpFileGetLength(spirv_file);
+	void *spirv   = wpMemAllocatorAlloc(&arena, (u64)spirv_len);
+	check(spirv != nullptr, EXIT_CODE_ALLOCATION_FAILURE);
+	wpFileRead(spirv, spirv_file, (u64)spirv_len);
+	wpFileClose(spirv_file);
 
-	Slang::ComPtr<slang::ISession> slang_session;
-	slang::SessionDesc session_desc = {};
-	session_desc.targets       = &target;
-	session_desc.targetCount   = 1;
-	session_desc.defaultMatrixLayoutMode = SLANG_MATRIX_LAYOUT_COLUMN_MAJOR;
-	app.slang_session->createSession(session_desc, slang_session.writeRef());
-
-	Slang::ComPtr<slang::IModule> slang_module {
-		slang_session->loadModuleFromSource("triangle", "assets/shader.slang", nullptr, nullptr),
-	};
-	Slang::ComPtr<slang::IBlob> spirv;
-	slang_module->getTargetCode(0, spirv.writeRef());
-	// }}}
-
-	// {{{ Create shader module
 	PrRhiShaderDesc shader_desc = {};
-	shader_desc.spirv_code      = spirv->getBufferPointer();
-	shader_desc.spirv_size      = spirv->getBufferSize();
+	shader_desc.spirv_code      = spirv;
+	shader_desc.spirv_size      = (u64)spirv_len;
 
 	app.shader = prRhiCreateShader(app.device, shader_desc);
 	// }}}
 
 	// {{{ Pipeline layout
 	PrRhiPushConstantRange pc_range = {};
-	pc_range.stage_flags            = PR_RHI_SHADER_STAGE_VERTEX;
-	pc_range.size                   = sizeof(u64);
+	pc_range.stage_flags            = (PrRhiShaderStage)(PR_RHI_SHADER_STAGE_VERTEX |
+	                                                     PR_RHI_SHADER_STAGE_FRAGMENT);
+	pc_range.size                   = sizeof(BlitData);
 
 	PrRhiDescriptorSetLayoutArray pl_layouts = wpArray(PrRhiDescriptorSetLayout *, app.desc_set_layout);
 
@@ -438,18 +359,6 @@ int main() {
 	// }}}
 
 	// {{{ Graphics pipeline
-	PrRhiVertexInputBindingArray vertex_bindings = wpArray(
-		PrRhiVertexInputBinding,
-		PrRhiVertexInputBinding{ 0, sizeof(Vertex) }
-	);
-
-	PrRhiVertexAttributeArray vertex_attrs = wpArray(
-		PrRhiVertexAttribute,
-		PrRhiVertexAttribute{ 0, 0, PR_RHI_FORMAT_R32G32B32_SFLOAT, 0 },
-		PrRhiVertexAttribute{ 1, 0, PR_RHI_FORMAT_R32G32B32_SFLOAT, offsetof(Vertex, normal) },
-		PrRhiVertexAttribute{ 2, 0, PR_RHI_FORMAT_R32G32_SFLOAT,    offsetof(Vertex, uv) }
-	);
-
 	PrRhiColorBlendAttachmentArray blend_attachments = wpArray(
 		PrRhiColorBlendAttachment,
 		PrRhiColorBlendAttachment{ 0xf }
@@ -457,37 +366,34 @@ int main() {
 
 	PrRhiFormatArray color_fmt_array = wpArray(PrRhiFormat, app.swapchain_format);
 
-	PrRhiGraphicsPipelineDesc pipe_desc   = {};
+	PrRhiGraphicsPipelineDesc pipe_desc = {};
 	pipe_desc.vertex_shader               = app.shader;
 	pipe_desc.vertex_shader_entry_point   = "main";
 	pipe_desc.fragment_shader             = app.shader;
 	pipe_desc.fragment_shader_entry_point = "main";
-	pipe_desc.vertex_bindings             = vertex_bindings;
-	pipe_desc.vertex_attributes           = vertex_attrs;
-	pipe_desc.topology                    = PR_RHI_TOPOLOGY_TRIANGLE_LIST;
+	pipe_desc.topology                    = PR_RHI_TOPOLOGY_TRIANGLE_STRIP;
 	pipe_desc.color_attachment_formats    = color_fmt_array;
 	pipe_desc.depth_attachment_format     = swap_desc.depth_format;
-	pipe_desc.depth_test_enable           = true;
-	pipe_desc.depth_write_enable          = true;
-	pipe_desc.depth_compare_op            = PR_RHI_COMPARE_OP_LESS_OR_EQUAL;
+	pipe_desc.depth_test_enable           = false;
+	pipe_desc.depth_write_enable          = false;
 	pipe_desc.blend_attachments           = blend_attachments;
 	pipe_desc.dynamic_viewport            = true;
 	pipe_desc.dynamic_scissor             = true;
-	pipe_desc.cull_mode                   = PR_RHI_CULL_MODE_BACK;
-	pipe_desc.front_face                  = PR_RHI_FRONT_FACE_COUNTER_CLOCKWISE;
+	pipe_desc.cull_mode                   = PR_RHI_CULL_MODE_NONE;
 	pipe_desc.line_width                  = 1.0f;
+	pipe_desc.multisample_count           = PR_RHI_SAMPLE_COUNT_1;
 	pipe_desc.layout                      = app.pipeline_layout;
 
 	app.pipeline = prRhiCreateGraphicsPipeline(app.device, pipe_desc);
 	// }}}
 
 	// {{{ Render loop
-	app.object_rotations = wpArrayAllocCapacity(glm::vec3, &arena, AppState::instance_count,
-	                                            WP_ARRAY_INIT_FILLED);
-	u64 last_time   = SDL_GetTicks();
-	SDL_Event event = {};
 	app.frame_index = 0;
+	app.selected    = 0;
 	u32 image_index = 0;
+	PrRhiTextureSize tex_size = prRhiGetTextureSize(app.textures[app.selected].texture);
+	std::cout << "Texture " << app.selected << ": " << TEXTURE_PATHS[app.selected]
+	          << " (" << tex_size.width << 'x' << tex_size.height << ")\n";
 
 	while (true) {
 		// {{{ Wait on fence
@@ -508,20 +414,11 @@ int main() {
 		if (app.update_swapchain) {
 			// Skip this frame — will recreate below
 		} else {
-			// {{{ Update shader data
-			app.shader_data.projection = glm::perspective(glm::radians(45.0f),
-			                                              (f32)app.window_size.x / (f32)app.window_size.y,
-			                                              0.1f, 32.0f);
-			app.shader_data.view = glm::translate(glm::mat4(1.0f), glm::vec3(0.0f, 0.0f, -6.0f));
-			for (i32 i = 0; i < (i32)AppState::instance_count; ++i) {
-				glm::vec3 instance_pos = glm::vec3((f32)(i - 1) * 3.0f, 0.0f, 0.0f);
-				app.shader_data.model[i] = glm::translate(glm::mat4(1.0f), instance_pos) *
-				                           glm::mat4_cast(glm::quat(app.object_rotations[i]));
-			}
-
-			void *shader_data_ptr = prRhiBufferMap(app.device, app.shader_data_bufs[app.frame_index]);
-			memcpy(shader_data_ptr, &app.shader_data, sizeof(ShaderData));
-			prRhiBufferUnmap(app.device, app.shader_data_bufs[app.frame_index]);
+			// {{{ Compute contain-fit rect
+			PrRhiTextureSize tex_size = prRhiGetTextureSize(app.textures[app.selected].texture);
+			f32 fit_rect[4] = {};
+			computeFitRect((f32)tex_size.width, (f32)tex_size.height,
+			               (f32)app.window_width, (f32)app.window_height, fit_rect);
 			// }}}
 
 			// {{{ Record command buffer
@@ -534,7 +431,6 @@ int main() {
 				PrRhiImageMemoryBarrierArray barriers_arr =
 					wpArrayWithCapacity(PrRhiImageMemoryBarrier, 2, WP_ARRAY_INIT_FILLED);
 
-				// Color attachment
 				PrRhiTexture *color_tex          = prRhiGetSwapchainTexture(app.swapchain, image_index);
 				barriers_arr[0].texture          = color_tex;
 				barriers_arr[0].old_layout       = PR_RHI_LAYOUT_UNDEFINED;
@@ -544,7 +440,6 @@ int main() {
 				barriers_arr[0].dst_stage_mask   = PR_RHI_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT;
 				barriers_arr[0].dst_access_mask  = (PrRhiAccess)(PR_RHI_ACCESS_COLOR_ATTACHMENT_READ | PR_RHI_ACCESS_COLOR_ATTACHMENT_WRITE);
 
-				// Depth attachment
 				PrRhiTexture *depth_tex          = prRhiGetSwapchainDepthTexture(app.swapchain);
 				barriers_arr[1].texture          = depth_tex;
 				barriers_arr[1].old_layout       = PR_RHI_LAYOUT_UNDEFINED;
@@ -578,8 +473,8 @@ int main() {
 				prRhiCmdBeginRendering(cb, color_arr, &depth_att);
 			}
 
-			prRhiCmdSetViewport(cb, 0.0f, 0.0f, (f32)app.window_size.x, (f32)app.window_size.y);
-			prRhiCmdSetScissor(cb, 0, 0, (u32)app.window_size.x, (u32)app.window_size.y);
+			prRhiCmdSetViewport(cb, 0.0f, 0.0f, (f32)app.window_width, (f32)app.window_height);
+			prRhiCmdSetScissor(cb, 0, 0, (u32)app.window_width, (u32)app.window_height);
 
 			prRhiCmdBindPipeline(cb, PR_RHI_PIPELINE_BIND_POINT_GRAPHICS, app.pipeline);
 
@@ -587,16 +482,34 @@ int main() {
 			prRhiCmdBindDescriptorSets(cb, PR_RHI_PIPELINE_BIND_POINT_GRAPHICS,
 			                           app.pipeline_layout, 0, sets);
 
-			PrRhiBufferArray vert_buf_arr = wpArray(PrRhiBuffer *, app.vert_index_buf);
-			WpU64Array vert_offsets       = wpArray(u64, 0);
-			prRhiCmdBindVertexBuffers(cb, 0, vert_buf_arr, vert_offsets);
-			prRhiCmdBindIndexBuffer(cb, app.vert_index_buf, app.vertex_buf_size, PR_RHI_INDEX_TYPE_UINT16);
+			// Draw background (fullscreen grey quad)
+			BlitData bg = {};
+			bg.rect[0] = -1.0f;
+			bg.rect[1] = -1.0f;
+			bg.rect[2] =  1.0f;
+			bg.rect[3] =  1.0f;
+			bg.selected = 0;
+			bg.mode     = 1;
+			prRhiCmdPushConstants(cb, app.pipeline_layout,
+			                      (PrRhiShaderStage)(PR_RHI_SHADER_STAGE_VERTEX |
+			                                         PR_RHI_SHADER_STAGE_FRAGMENT),
+			                      0, sizeof(BlitData), &bg);
+			prRhiCmdDraw(cb, 4, 1, 0, 0);
 
-			// Push shader data buffer device address
-			u64 buf_addr = prRhiGetBufferDeviceAddress(app.device, app.shader_data_bufs[app.frame_index]);
-			prRhiCmdPushConstants(cb, app.pipeline_layout, PR_RHI_SHADER_STAGE_VERTEX, 0, sizeof(u64), &buf_addr);
+			// Draw texture (contain-fit)
+			BlitData blit = {};
+			blit.rect[0] = fit_rect[0];
+			blit.rect[1] = fit_rect[1];
+			blit.rect[2] = fit_rect[2];
+			blit.rect[3] = fit_rect[3];
+			blit.selected = app.selected;
+			blit.mode     = 0;
+			prRhiCmdPushConstants(cb, app.pipeline_layout,
+			                      (PrRhiShaderStage)(PR_RHI_SHADER_STAGE_VERTEX |
+			                                         PR_RHI_SHADER_STAGE_FRAGMENT),
+			                      0, sizeof(BlitData), &blit);
 
-			prRhiCmdDrawIndexed(cb, (u32)app.index_count, AppState::instance_count, 0, 0, 0);
+			prRhiCmdDraw(cb, 4, 1, 0, 0);
 			prRhiCmdEndRendering(cb);
 
 			// Transition to present
@@ -632,33 +545,28 @@ int main() {
 		}
 
 		// {{{ Poll events
-		f32 elapsed_time = (SDL_GetTicks() - last_time) / 1000.0f;
-		last_time = SDL_GetTicks();
+		SDL_Event event = {};
 		while (SDL_PollEvent(&event)) {
 			switch (event.type) {
 				case SDL_EVENT_QUIT:
-					app.update_swapchain = false;  // signal exit — use update_swapchain flag
 					goto done;
 				case SDL_EVENT_KEY_DOWN:
 					if (event.key.key == SDLK_ESCAPE) goto done;
 					if (event.key.key == SDLK_PLUS || event.key.key == SDLK_KP_PLUS || event.key.key == SDLK_EQUALS) {
-						app.shader_data.selected = (app.shader_data.selected < 2) ? app.shader_data.selected + 1 : 0;
+						app.selected = (app.selected + 1) % AppState::texture_count;
+						PrRhiTextureSize ts = prRhiGetTextureSize(app.textures[app.selected].texture);
+						std::cout << "Texture " << app.selected << ": " << TEXTURE_PATHS[app.selected]
+						          << " (" << ts.width << 'x' << ts.height << ")\n";
 					}
 					if (event.key.key == SDLK_MINUS || event.key.key == SDLK_KP_MINUS) {
-						app.shader_data.selected = (app.shader_data.selected > 0) ? app.shader_data.selected - 1 : 2;
+						app.selected = (app.selected + AppState::texture_count - 1) % AppState::texture_count;
+						PrRhiTextureSize ts = prRhiGetTextureSize(app.textures[app.selected].texture);
+						std::cout << "Texture " << app.selected << ": " << TEXTURE_PATHS[app.selected]
+						          << " (" << ts.width << 'x' << ts.height << ")\n";
 					}
 					break;
-				case SDL_EVENT_MOUSE_MOTION:
-					if (event.button.button == SDL_BUTTON_LEFT) {
-						app.object_rotations[app.shader_data.selected].x -= (f32)event.motion.yrel * elapsed_time;
-						app.object_rotations[app.shader_data.selected].y += (f32)event.motion.xrel * elapsed_time;
-					}
-					break;
-				case SDL_EVENT_MOUSE_WHEEL:
-					// Camera position handled via shader_data update in loop
-					break;
 				case SDL_EVENT_WINDOW_RESIZED:
-					check(SDL_GetWindowSize(app.window, &app.window_size.x, &app.window_size.y),
+					check(SDL_GetWindowSizeInPixels(app.window, &app.window_width, &app.window_height),
 					      EXIT_CODE_GET_WINDOW_SIZE_FAILED);
 					app.update_swapchain = true;
 					break;
@@ -670,12 +578,14 @@ int main() {
 		if (app.update_swapchain) {
 			prRhiDeviceWaitIdle(app.device);
 			prRhiRecreateSwapchain(app.device, &app.swapchain,
-			                        (u32)app.window_size.x, (u32)app.window_size.y);
+			                        (u32)app.window_width, (u32)app.window_height);
 
-			// Re-create render completed semaphores for new image count
-			// TODO: proper cleanup — for now, just leak old ones
-			u32 new_count = 0;
-			prRhiAcquireNextImage(app.device, app.swapchain, NULL, &new_count);
+			// Re-create render completed semaphores for the new image count
+			u32 new_count = prRhiGetSwapchainImageCount(app.swapchain);
+			for (u32 i = 0; i < app.render_semaphore_count; ++i) {
+				prRhiDestroySemaphore(app.device, app.render_completed_semaphores[i]);
+			}
+			app.render_semaphore_count = new_count;
 			app.render_completed_semaphores = wpArrayAllocCapacity(PrRhiSemaphore *, &arena,
 			                                                        new_count, WP_ARRAY_INIT_FILLED);
 			for (u32 i = 0; i < new_count; ++i) {
@@ -708,15 +618,13 @@ int main() {
 	prRhiFreeCommandBuffers(app.device, app.cmd_pool, app.cmd_buffers);
 	prRhiDestroyCommandPool(app.device, app.cmd_pool);
 
-	for (u32 i = 0; i < swapchain_image_count; ++i) {
+	for (u32 i = 0; i < app.render_semaphore_count; ++i) {
 		prRhiDestroySemaphore(app.device, app.render_completed_semaphores[i]);
 	}
 	for (u32 i = 0; i < AppState::max_frames_in_flight; ++i) {
 		prRhiDestroySemaphore(app.device, app.image_acquired_semaphores[i]);
 		prRhiDestroyFence(app.device, app.fences[i]);
-		prRhiDestroyBuffer(app.device, app.shader_data_bufs[i]);
 	}
-	prRhiDestroyBuffer(app.device, app.vert_index_buf);
 
 	prRhiDestroySwapchain(app.device, app.swapchain);
 	prRhiDestroyDevice(app.device);

src/prism/rhi/pr_rhi.h

@@ -111,6 +111,7 @@ PrRhiTexture *prRhiCreateTexture(PrRhiDevice *device, PrRhiTextureDesc desc);
 PrRhiTexture *prRhiCreateTextureFromKtx(PrRhiDevice *device, const char *path,
                                           PrRhiCommandPool *pool, PrRhiCommandBuffer *cb);
 void          prRhiDestroyTexture(PrRhiDevice *device, PrRhiTexture *texture);
+PrRhiTextureSize prRhiGetTextureSize(PrRhiTexture *texture);
 
 // ======================================================================
 // Samplers

src/prism/rhi/pr_rhi_types.h

@@ -352,6 +352,11 @@ typedef struct PrRhiShaderDesc {
 	u64         spirv_size;
 } PrRhiShaderDesc;
 
+typedef struct PrRhiTextureSize {
+	u32 width;
+	u32 height;
+} PrRhiTextureSize;
+
 typedef struct PrRhiPipelineLayoutDesc {
 	PrRhiDescriptorSetLayoutArray set_layouts;
 	PrRhiPushConstantRangeArray   push_constant_ranges;

src/prism/rhi/vulkan/pr_rhi_vk.c

@@ -834,7 +834,9 @@ PrRhiSwapchainResult prRhiAcquireNextImageVk(PrRhiDevice *device, PrRhiSwapchain
 	VkSemaphore vk_semaphore = signal_semaphore ? signal_semaphore->handle : VK_NULL_HANDLE;
 	VkResult res = vkAcquireNextImageKHR(device->handle, swapchain->handle, UINT64_MAX, vk_semaphore,
 	                                     VK_NULL_HANDLE, &swapchain->current_image_index);
-	if (res == VK_ERROR_OUT_OF_DATE_KHR) { return PR_RHI_SWAPCHAIN_OUT_OF_DATE; }
+	if (res == VK_ERROR_OUT_OF_DATE_KHR || res == VK_SUBOPTIMAL_KHR) {
+		return PR_RHI_SWAPCHAIN_OUT_OF_DATE;
+	}
 	_checkVk(res, "vkAcquireNextImageKHR");
 	if (out_image_index) { *out_image_index = swapchain->current_image_index; }
 	return PR_RHI_SWAPCHAIN_SUCCESS;
@@ -854,7 +856,9 @@ PrRhiSwapchainResult prRhiPresentVk(PrRhiDevice *device, PrRhiSwapchain *swapcha
 	};
 
 	VkResult res = vkQueuePresentKHR(device->queue, &present_info);
-	if (res == VK_ERROR_OUT_OF_DATE_KHR) { return PR_RHI_SWAPCHAIN_OUT_OF_DATE; }
+	if (res == VK_ERROR_OUT_OF_DATE_KHR || res == VK_SUBOPTIMAL_KHR) {
+		return PR_RHI_SWAPCHAIN_OUT_OF_DATE;
+	}
 	_checkVk(res, "vkQueuePresentKHR");
 	return PR_RHI_SWAPCHAIN_SUCCESS;
 }
@@ -866,13 +870,22 @@ void prRhiRecreateSwapchainVk(PrRhiDevice *device, PrRhiSwapchain **swapchain,
 
 	VkDevice vk_device       = device->handle;
 	VkPhysicalDevice vk_pdev = device->physical_device;
+	VkSurfaceKHR vk_surface  = ((PrRhiSurface *)old->surface)->handle;
 
-	VkExtent2D extent = { width, height };
+	VkSurfaceCapabilitiesKHR caps = {};
+	_checkVk(vkGetPhysicalDeviceSurfaceCapabilitiesKHR(vk_pdev, vk_surface, &caps),
+	         "vkGetPhysicalDeviceSurfaceCapabilitiesKHR");
+
+	VkExtent2D extent = caps.currentExtent;
+	if (extent.width == 0xffffffff) {
+		extent.width  = width;
+		extent.height = height;
+	}
 
 	VkSwapchainCreateInfoKHR swapchain_info = {
 		.sType            = VK_STRUCTURE_TYPE_SWAPCHAIN_CREATE_INFO_KHR,
 		.oldSwapchain     = old->handle,
-		.surface          = ((PrRhiSurface *)old->surface)->handle,
+		.surface          = vk_surface,
 		.minImageCount    = old->image_count,
 		.imageFormat      = (VkFormat)old->format,
 		.imageColorSpace  = _default_colorspace,
@@ -1315,6 +1328,14 @@ PrRhiTexture *prRhiCreateTextureFromKtxVk(PrRhiDevice *device, const char *path,
 	return texture;
 }
 
+PrRhiTextureSize prRhiGetTextureSizeVk(PrRhiTexture *texture) {
+	PrRhiTextureSize size = {};
+	if (!texture) { return size; }
+	size.width  = texture->width;
+	size.height = texture->height;
+	return size;
+}
+
 void prRhiDestroyTextureVk(PrRhiDevice *device, PrRhiTexture *texture) {
 	if (!texture) { return; }
 	VkDevice vk_device = device->handle;

src/prism/rhi/vulkan/pr_rhi_vk.h

@@ -166,6 +166,7 @@ PrRhiTexture *prRhiCreateTextureVk(PrRhiDevice *device, PrRhiTextureDesc desc);
 PrRhiTexture *prRhiCreateTextureFromKtxVk(PrRhiDevice *device, const char *path,
                                             PrRhiCommandPool *pool, PrRhiCommandBuffer *cb);
 void          prRhiDestroyTextureVk(PrRhiDevice *device, PrRhiTexture *texture);
+PrRhiTextureSize prRhiGetTextureSizeVk(PrRhiTexture *texture);
 
 PrRhiSampler *prRhiCreateSamplerVk(PrRhiDevice *device, PrRhiSamplerDesc desc);
 void          prRhiDestroySamplerVk(PrRhiDevice *device, PrRhiSampler *sampler);

src/prism/rhi/vulkan/pr_rhi_vk_aliases.h

@@ -35,6 +35,7 @@
 #define prRhiCreateTexture                 prRhiCreateTextureVk
 #define prRhiCreateTextureFromKtx          prRhiCreateTextureFromKtxVk
 #define prRhiDestroyTexture                prRhiDestroyTextureVk
+#define prRhiGetTextureSize                prRhiGetTextureSizeVk
 #define prRhiCreateSampler                 prRhiCreateSamplerVk
 #define prRhiDestroySampler                prRhiDestroySamplerVk
 #define prRhiCreateShader                  prRhiCreateShaderVk