From 5a24809935a2abcc293e10f7dad8b5fcc98c8f95 Mon Sep 17 00:00:00 2001
From: Abdelrahman <said.abdelrahman89@gmail.com>
Date: Sun, 28 Jul 2024 22:43:00 +0100
Subject: [PATCH] Initial implementatin of barycentric coordinates

---
 src/main.c |  6 +++--
 src/obj.c  | 78 +++++++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 79 insertions(+), 5 deletions(-)

diff --git a/src/main.c b/src/main.c
index e27ab03..6a965aa 100644
--- a/src/main.c
+++ b/src/main.c
@@ -21,19 +21,21 @@ int main(void) {
   }
 
   Colour bg = {.r = 42, .g = 45, .b = 52, .a = 255};
+  Colour teal = {.r = 14, .g = 156, .b = 208, .a = 255};
   Colour orange = {.r = 242, .g = 100, .b = 48, .a = 255};
   Image img = {.width = 1200, .height = 1200};
   if (!init_image(arena, &img)) {
     return TINY_EXIT_IMAGE_INIT_FAILED;
   }
 
-  Model model = load_obj_file(arena, "resources/head.obj");
+  Model model = load_obj_file(arena, "resources/triangle.obj");
   if (IS_NULL_MODEL(model)) {
     return TINY_EXIT_MODEL_LOAD_FAILED;
   }
 
   clear_image(&img, bg);
-  render_model(&model, &img, orange, RENDER_TYPE_FILLED);
+  render_model(&model, &img, teal, RENDER_TYPE_FILLED);
+  render_model(&model, &img, orange, RENDER_TYPE_WIREFRAME);
   save_image(&img, "result.pam");
 
   wapp_mem_arena_destroy(&arena);
diff --git a/src/obj.c b/src/obj.c
index e2ce4fb..594e3a8 100644
--- a/src/obj.c
+++ b/src/obj.c
@@ -16,10 +16,42 @@ struct triangle_bbox {
   u64 y1;
 };
 
+typedef struct i64x2 V2i;
+struct i64x2 {
+  i64 x;
+  i64 y;
+};
+
+typedef struct f32x3 V3f;
+struct f32x3 {
+  f32 x;
+  f32 y;
+  f32 z;
+};
+
+typedef struct u64x3 V3u;
+struct u64x3 {
+  u64 x;
+  u64 y;
+  u64 z;
+};
+
+typedef struct f32_3x3 M3x3f;
+struct f32_3x3 {
+  V3f row0;
+  V3f row1;
+  V3f row2;
+};
+
 internal void render_triangle(const Triangle *triangle, const Model *model,
                               Image *img, Colour colour, RenderType type);
+internal void fill_triangle(Image *img, Vertex vertices[TRIANGLE_VERTICES],
+                            Colour colour);
 internal TriangleBBox get_triangle_bbox(const Image *img,
                                         Vertex vertices[TRIANGLE_VERTICES]);
+internal V3f get_barycentric_coords(f32 d00, f32 d01, f32 d11, f32 denom,
+                                    const V2i *ab, const V2i *ac,
+                                    const V2i *ap);
 internal void get_image_coordinates(const Vertex *vertex, const Image *img,
                                     u64 *x, u64 *y);
 internal u64 ndc_to_image_coordinate(f32 value, u64 max);
@@ -104,9 +136,36 @@ internal void render_triangle(const Triangle *triangle, const Model *model,
       draw_line(img, x0, y0, x1, y1, colour);
     }
   } else if (type == RENDER_TYPE_FILLED) {
-    TriangleBBox bbox = get_triangle_bbox(img, vertices);
-    for (u64 y = bbox.y0; y < bbox.y1; ++y) {
-      draw_line(img, bbox.x0, y, bbox.x1, y, colour);
+    fill_triangle(img, vertices, colour);
+  }
+}
+
+internal void fill_triangle(Image *img, Vertex vertices[TRIANGLE_VERTICES],
+                            Colour colour) {
+  TriangleBBox bbox = get_triangle_bbox(img, vertices);
+
+  u64 v0x, v0y, v1x, v1y, v2x, v2y;
+  get_image_coordinates(&(vertices[0]), img, &v0x, &v0y);
+  get_image_coordinates(&(vertices[1]), img, &v1x, &v1y);
+  get_image_coordinates(&(vertices[2]), img, &v2x, &v2y);
+
+  V2i ab = {.x = (i64)v1x - (i64)v0x, .y = (i64)v1y - (i64)v0y};
+  V2i ac = {.x = (i64)v2x - (i64)v0x, .y = (i64)v2y - (i64)v0y};
+  f32 d00 = (f32)ab.x * (f32)ab.x + (f32)ab.y + (f32)ab.y;
+  f32 d01 = (f32)ab.x * (f32)ac.x + (f32)ab.y + (f32)ac.y;
+  f32 d11 = (f32)ac.x * (f32)ac.x + (f32)ac.y + (f32)ac.y;
+  f32 denom = (f32)d00 * (f32)d11 - (f32)d01 * (f32)d01;
+  V2i ap;
+  V3f coords;
+
+  for (u64 y = bbox.y0; y < bbox.y1; ++y) {
+    for (u64 x = bbox.x0; x < bbox.x1; ++x) {
+      ap = (V2i){.x = (i64)x - (i64)v0x, .y = (i64)y - (i64)v0y};
+      coords = get_barycentric_coords(d00, d01, d11, denom, &ab, &ac, &ap);
+      if (coords.x < 0.0f || coords.y < 0.0f || coords.z < 0.0f) {
+        continue;
+      }
+      set_pixel(img, x, y, colour);
     }
   }
 }
@@ -128,6 +187,19 @@ internal TriangleBBox get_triangle_bbox(const Image *img,
   };
 }
 
+internal V3f get_barycentric_coords(f32 d00, f32 d01, f32 d11, f32 denom,
+                                    const V2i *ab, const V2i *ac,
+                                    const V2i *ap) {
+  f32 d20 = (f32)ap->x * (f32)ab->x + (f32)ap->y + (f32)ab->y;
+  f32 d21 = (f32)ap->x * (f32)ac->x + (f32)ap->y + (f32)ac->y;
+
+  f32 v = (d11 * d20 - d01 * d21) / denom;
+  f32 w = (d00 * d21 - d01 * d20) / denom;
+  f32 u = 1.0f - v - w;
+
+  return (V3f){v, w, u};
+}
+
 internal void get_image_coordinates(const Vertex *vertex, const Image *img,
                                     u64 *x, u64 *y) {
   *x = ndc_to_image_coordinate(vertex->x, img->width);