Add shading

src/main.c

@@ -37,8 +37,9 @@ int main(void) {
   }
 
   clear_image(&img, bg);
-  render_model(&model, &img, teal, RENDER_TYPE_FILLED, COLOUR_TYPE_RANDOM);
+  render_model(&model, &img, teal, RENDER_TYPE_SHADED, COLOUR_TYPE_FIXED);
-  render_model(&model, &img, orange, RENDER_TYPE_WIREFRAME, COLOUR_TYPE_FIXED);
+  // render_model(&model, &img, orange, RENDER_TYPE_WIREFRAME,
+  // COLOUR_TYPE_FIXED);
   save_image(&img, "result.pam");
 
   wapp_mem_arena_destroy(&arena);

src/obj.c

@@ -5,15 +5,33 @@
 #include "typed_list.h"
 #include "utils.h"
 #include <limits.h>
+#include <math.h>
 #include <stdio.h>
 #include <stdlib.h>
 
 #define TRIANGLE_VERTICES 3
+
+#define V2(T, ELEM_T, X0, Y0, X1, Y1)                                          \
+  ((T){(ELEM_T)X1 - (ELEM_T)X0, (ELEM_T)Y1 - (ELEM_T)Y0})
+#define V3(T, ELEM_T, X0, Y0, Z0, X1, Y1, Z1)                                  \
+  ((T){(ELEM_T)X1 - (ELEM_T)X0, (ELEM_T)Y1 - (ELEM_T)Y0,                       \
+       (ELEM_T)Z1 - (ELEM_T)Z0})
 #define dot_v2(V1, V2) ((f32)V1.x * (f32)V2.x + (f32)V1.y * (f32)V2.y)
 #define dot_v3(V1, V2)                                                         \
   ((f32)V1.x * (f32)V2.x + (f32)V1.y * (f32)V2.y + (f32)V1.z * (f32)V2.z)
-#define V2(T, ELEM_T, X0, Y0, X1, Y1)                                          \
+#define normalise_v3(V)                                                        \
-  ((T){(ELEM_T)X1 - (ELEM_T)X0, (ELEM_T)Y1 - (ELEM_T)Y0})
+  do {                                                                         \
+    f32 magnitude = sqrtf(dot_v3(V, V));                                       \
+    V.x /= magnitude;                                                          \
+    V.y /= magnitude;                                                          \
+    V.z /= magnitude;                                                          \
+  } while (0);
+#define cross_product(V1, V2)                                                  \
+  ((V3f){                                                                      \
+      .x = V1.y * V2.z - V1.z * V2.y,                                          \
+      .y = V1.z * V2.x - V1.x * V2.z,                                          \
+      .z = V1.x * V2.y - V1.y * V2.x,                                          \
+  })
 
 typedef struct triangle_bbox TriangleBBox;
 struct triangle_bbox {
@@ -63,6 +81,8 @@ 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);
 
+V3f g_light_dir = {0.0f, 0.0f, -1.0f};
+
 Model load_obj_file(Arena *arena, const char *filename) {
   if (!arena) {
     return NULL_MODEL;
@@ -148,9 +168,29 @@ internal void render_triangle(const Triangle *triangle, const Model *model,
 
       draw_line(img, x0, y0, x1, y1, colour);
     }
-  } else if (type == RENDER_TYPE_FILLED) {
+  } else if (type == RENDER_TYPE_FILLED || type == RENDER_TYPE_SHADED) {
+    f32 intensity = 1.0f;
+
+    if (type == RENDER_TYPE_SHADED) {
+      V3f ab = V3(V3f, f32, vertices[0].x, vertices[0].y, vertices[0].z,
+                  vertices[1].x, vertices[1].y, vertices[1].z);
+      V3f ac = V3(V3f, f32, vertices[0].x, vertices[0].y, vertices[0].z,
+                  vertices[2].x, vertices[2].y, vertices[2].z);
+
+      V3f normal = cross_product(ac, ab);
+      normalise_v3(normal);
+
+      intensity = dot_v3(normal, g_light_dir);
+
+      colour.r *= intensity;
+      colour.g *= intensity;
+      colour.b *= intensity;
+    }
+
+    if (intensity > 0.0f) {
       fill_triangle(img, vertices, colour);
     }
+  }
 }
 
 internal void fill_triangle(Image *img, Vertex vertices[TRIANGLE_VERTICES],

src/obj.h

@@ -26,6 +26,7 @@ struct triangle {
 typedef enum {
   RENDER_TYPE_WIREFRAME,
   RENDER_TYPE_FILLED,
+  RENDER_TYPE_SHADED,
 
   COUNT_RENDER_TYPES,
 } RenderType;