feat(assets): size and tint debug raster passes in the vertex shader

assets/shaders/cube.vert

@@ -8,13 +8,24 @@ layout(location = 0) out vec3 frag_color;
 
 layout(push_constant) uniform PushConstants {
     mat4 mvp;
+    // xyz is the chunk's world offset; w is the debug-tint weight, 0.0 for normal rendering and 1.0 for a debug raster pass.
     vec4 chunk_offset;
 } push_constants;
 
+// Colour applied to debug raster passes, chosen to contrast with terrain and to remain legible when overlaid on filled geometry.
+const vec3 DEBUG_COLOR = vec3(1.0, 0.0, 1.0);
+
+// Size, in pixels, of the points emitted under VK_POLYGON_MODE_POINT. Sizes above 1.0 require the largePoints device feature.
+const float DEBUG_POINT_SIZE = 5.0;
+
 void main() {
     // The chunk-local vertex is shifted into world space by the per-chunk offset before projection.
     vec3 world_position = in_position + push_constants.chunk_offset.xyz;
     gl_Position = push_constants.mvp * vec4(world_position, 1.0);
 
-    frag_color = in_color;
+    // Point size is consulted whenever the polygon mode is POINT; leaving it unwritten renders points of undefined size. It is ignored by the FILL and LINE pipelines, so it is written unconditionally.
+    gl_PointSize = DEBUG_POINT_SIZE;
+
+    float debug_tint = push_constants.chunk_offset.w;
+    frag_color = mix(in_color, DEBUG_COLOR, debug_tint);
 }

assets/shaders/cube.vert.spv

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:e96757ea7c663e85f5bb366e9475eb3621a1477c0c2afbef33c3a33a99564de8
+oid sha256:17461a207a6e1d6ba3e2b050aaa83ad0fb880a29e54e42295a1d43cbdfbdc115
-size 1576
+size 1888