Switch to using a viewport matrix

src/obj.c

@@ -13,6 +13,7 @@
 
 #define TRIANGLE_VERTICES 3
 #define CAMERA_DISTANCE 5.0f
+#define DEPTH_MAX 255
 
 #define V2(T, ELEM_T, X0, Y0, X1, Y1)                                          \
   ((T){(ELEM_T)X1 - (ELEM_T)X0, (ELEM_T)Y1 - (ELEM_T)Y0})
@@ -106,14 +107,13 @@ internal void fill_triangle(Render *render, V3f vertices[TRIANGLE_VERTICES],
                             V2f coordinates[TRIANGLE_VERTICES], Colour colour,
                             Image *texture, RenderType type);
 internal M4x4f lookat(V3f eye, V3f target, V3f up);
+internal M4x4f viewport(f32 x, f32 y, u64 w, u64 h);
 internal TriangleBBox get_triangle_bbox(const Image *img,
                                         V3f 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(f32 norm_x, f32 norm_y, const Image *img,
+internal V3f get_viewport_vertex(V3f 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};
 
@@ -293,14 +293,15 @@ internal void render_triangle(const Triangle *triangle, const Model *model,
   if (type == RENDER_TYPE_WIREFRAME) {
     V3f v0, v1;
     u64 x0, y0, x1, y1;
+    V3f vp0, vp1;
     for (u64 i = 0; i < TRIANGLE_VERTICES; ++i) {
       v0 = vertices[i];
       v1 = vertices[(i + 1) % TRIANGLE_VERTICES];
 
-      get_image_coordinates(v0.x, v0.y, img, &x0, &y0);
+      vp0 = get_viewport_vertex(v0, img);
-      get_image_coordinates(v1.x, v1.y, img, &x1, &y1);
+      vp1 = get_viewport_vertex(v1, img);
 
-      draw_line(img, x0, y0, x1, y1, colour);
+      draw_line(img, (u64)vp0.x, (u64)vp0.y, (u64)vp1.x, (u64)vp1.y, colour);
     }
   } else if (type == RENDER_TYPE_FILLED || type == RENDER_TYPE_SHADED) {
     fill_triangle(render, vertices, normals, coordinates, colour,
@@ -316,10 +317,9 @@ internal void fill_triangle(Render *render, V3f vertices[TRIANGLE_VERTICES],
   Depth *depth = &(render->depth);
   TriangleBBox bbox = get_triangle_bbox(img, vertices);
 
-  V2u v0, v1, v2;
+  V3f v0 = get_viewport_vertex(vertices[0], img);
-  get_image_coordinates(vertices[0].x, vertices[0].y, img, &(v0.x), &(v0.y));
+  V3f v1 = get_viewport_vertex(vertices[1], img);
-  get_image_coordinates(vertices[1].x, vertices[1].y, img, &(v1.x), &(v1.y));
+  V3f v2 = get_viewport_vertex(vertices[2], img);
-  get_image_coordinates(vertices[2].x, vertices[2].y, img, &(v2.x), &(v2.y));
 
   V2i ab = V2(V2i, i64, v0.x, v0.y, v1.x, v1.y);
   V2i ac = V2(V2i, i64, v0.x, v0.y, v2.x, v2.y);
@@ -416,6 +416,22 @@ internal M4x4f lookat(V3f eye, V3f target, V3f up) {
   return mat4x4_mul(rotation, translation);
 }
 
+internal M4x4f viewport(f32 x, f32 y, u64 w, u64 h) {
+  M4x4f output = mat4x4_identity;
+
+  f32 half_width = (f32)w * 0.5f;
+  f32 half_height = (f32)h * 0.5f;
+  f32 half_depth = (f32)DEPTH_MAX * 0.5f;
+
+  output.row0.x = half_width;
+  output.row0.w = x + half_width;
+  output.row1.y = half_height;
+  output.row1.w = y + half_height;
+  output.row2.z = output.row2.w = half_depth;
+
+  return output;
+}
+
 internal TriangleBBox get_triangle_bbox(const Image *img,
                                         V3f vertices[TRIANGLE_VERTICES]) {
   f32 x0 = min(vertices[0].x, min(vertices[1].x, vertices[2].x));
@@ -425,11 +441,15 @@ internal TriangleBBox get_triangle_bbox(const Image *img,
   f32 y0 = max(vertices[0].y, max(vertices[1].y, vertices[2].y));
   f32 y1 = min(vertices[0].y, min(vertices[1].y, vertices[2].y));
 
-  TriangleBBox bbox = {0};
+  V3f minimum = get_viewport_vertex((V3f){x0, y0, 0.0f}, img);
-  get_image_coordinates(x0, y0, img, &(bbox.x0), &(bbox.y0));
+  V3f maximum = get_viewport_vertex((V3f){x1, y1, 0.0f}, img);
-  get_image_coordinates(x1, y1, img, &(bbox.x1), &(bbox.y1));
 
-  return bbox;
+  return (TriangleBBox){
+      .x0 = minimum.x,
+      .y0 = minimum.y,
+      .x1 = maximum.x,
+      .y1 = maximum.y,
+  };
 }
 
 internal V3f get_barycentric_coords(f32 d00, f32 d01, f32 d11, f32 denom,
@@ -449,20 +469,8 @@ internal V3f get_barycentric_coords(f32 d00, f32 d01, f32 d11, f32 denom,
   return (V3f){v, w, u};
 }
 
-internal void get_image_coordinates(f32 norm_x, f32 norm_y, const Image *img,
+internal V3f get_viewport_vertex(V3f vertex, const Image *img) {
-                                    u64 *x, u64 *y) {
+  V4f vh = {.x = vertex.x, .y = 0.0f - vertex.y, .z = vertex.z, .w = 1.0f};
-  *x = ndc_to_image_coordinate(norm_x, img->width);
+  vh = mat4x4_mul_vec4(viewport(vh.x, vh.y, img->width, img->height), vh);
-  *y = ndc_to_image_coordinate(0.0f - norm_y, img->height);
+  return project_vec4(vh);
-
-  if (*x >= img->width) {
-    *x = img->width - 1;
-  }
-  if (*y >= img->height) {
-    *y = img->height - 1;
-  }
-}
-
-internal u64 ndc_to_image_coordinate(f32 value, u64 max) {
-  f32 result = (value + 1.0f) * max * 0.5f;
-  return clamp((u64)result, 0, max);
 }