From 94287ff081a7c04c7a13409b1bf86bd787410a74 Mon Sep 17 00:00:00 2001
From: Abdelrahman <said.abdelrahman89@gmail.com>
Date: Sun, 14 Jul 2024 01:19:12 +0100
Subject: [PATCH] Switch to 1/z for depth buffering

---
 src/rasteriser/rasteriser.c | 10 +++++-----
 src/window/window.c         |  5 ++---
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/src/rasteriser/rasteriser.c b/src/rasteriser/rasteriser.c
index add5b5a..09d2578 100644
--- a/src/rasteriser/rasteriser.c
+++ b/src/rasteriser/rasteriser.c
@@ -130,9 +130,9 @@ internal void render_instance(window_t *wnd, const rasteriser_scene_t *scene,
         .h0 = v0.h,
         .h1 = v1.h,
         .h2 = v2.h,
-        .z0 = v0.position.z,
-        .z1 = v1.position.z,
-        .z2 = v2.position.z,
+        .z0 = 1.0f / v0.position.z,
+        .z1 = 1.0f / v1.position.z,
+        .z2 = 1.0f / v2.position.z,
         .colour = triangle.colour,
     };
 
@@ -228,7 +228,7 @@ void draw_filled_triangle(window_t *wnd, Arena *arena, triangle_t triangle) {
       current_z = get_z_pixel(wnd, x, y);
       new_z = list_get(z_segment, x - xl);
 
-      if (new_z <= current_z) {
+      if (new_z > current_z) {
         set_z_pixel(wnd, x, y, new_z);
         set_pixel(wnd, x, y, triangle.colour);
       }
@@ -322,7 +322,7 @@ void draw_shaded_triangle(window_t *wnd, Arena *arena, triangle_t triangle) {
       current_z = get_z_pixel(wnd, x, y);
       new_z = list_get(z_segment, x - xl);
 
-      if (new_z <= current_z) {
+      if (new_z > current_z) {
         set_z_pixel(wnd, x, y, new_z);
         set_pixel(wnd, x, y, shaded_colour);
       }
diff --git a/src/window/window.c b/src/window/window.c
index 5724b13..89c2778 100644
--- a/src/window/window.c
+++ b/src/window/window.c
@@ -7,7 +7,6 @@
 #include <SDL2/SDL_error.h>
 #include <SDL2/SDL_pixels.h>
 #include <SDL2/SDL_surface.h>
-#include <math.h>
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -107,7 +106,7 @@ void clear_window(window_t *wnd, colour_t colour) {
 
   for (u32 i = 0; i < count; ++i) {
     pixels[i] = colour.colour;
-    wnd->z_buffer[i] = INFINITY;
+    wnd->z_buffer[i] = 0.0f;
   }
 
   SDL_UnlockSurface(wnd->back_buffer);
@@ -141,7 +140,7 @@ f32 get_z_pixel(const window_t *wnd, i32 x, i32 y) {
   vec2i_t coords = denormalised_coords(wnd, x, y);
 
   if (coords.x < 0 || coords.y < 0) {
-    return INFINITY;
+    return 0.0f;
   }
 
   u32 index = index_from_coordinates(wnd, (u32)(coords.x), (u32)(coords.y));