initial mask impl

src/render/shader.wgsl

@@ -20,10 +20,22 @@ struct TextureInfo {
     sampler_idx: u32,
 }
 
+struct Mask {
+    top_left: UiVec2,
+    bot_right: UiVec2,
+}
+
+struct UiVec2 {
+    rel: vec2<f32>,
+    abs: vec2<f32>,
+}
+
 @group(2) @binding(0)
 var views: binding_array<texture_2d<f32>>;
 @group(2) @binding(1)
 var samplers: binding_array<sampler>;
+@group(2) @binding(2)
+var<storage> masks: array<Mask>;
 
 struct WindowUniform {
     dim: vec2<f32>,
@@ -36,6 +48,7 @@ struct InstanceInput {
     @location(3) bottom_right_offset: vec2<f32>,
     @location(4) binding: u32,
     @location(5) idx: u32,
+    @location(6) mask_idx: u32,
 }
 
 struct VertexOutput {
@@ -44,6 +57,7 @@ struct VertexOutput {
     @location(2) uv: vec2<f32>,
     @location(3) binding: u32,
     @location(4) idx: u32,
+    @location(5) mask_idx: u32,
     @builtin(position) clip_position: vec4<f32>,
 };
 
@@ -76,6 +90,7 @@ fn vs_main(
     out.idx = in.idx;
     out.top_left = top_left;
     out.bot_right = bot_right;
+    out.mask_idx = in.mask_idx;
 
     return out;
 }
@@ -87,17 +102,27 @@ fn fs_main(
     let pos = in.clip_position.xy;
     let region = Region(pos, in.uv, in.top_left, in.bot_right);
     let i = in.idx;
+    var color: vec4<f32>;
     switch in.binding {
         case RECT: {
-            return draw_rounded_rect(region, rects[i]);
+            color = draw_rounded_rect(region, rects[i]);
         }
         case TEXTURE: {
-            return draw_texture(region, textures[i]);
+            color = draw_texture(region, textures[i]);
         }
         default: {
-            return vec4(1.0, 0.0, 1.0, 1.0);
+            color = vec4(1.0, 0.0, 1.0, 1.0);
         }
     }
+    if in.mask_idx != 4294967295u {
+        let mask = masks[in.mask_idx];
+        let top_left = floor(mask.top_left.rel * window.dim) + floor(mask.top_left.abs);
+        let bot_right = floor(mask.bot_right.rel * window.dim) + floor(mask.bot_right.abs);
+        if pos.x < top_left.x || pos.x > bot_right.x || pos.y < top_left.y || pos.y > bot_right.y {
+            color *= 0.0;
+        }
+    }
+    return color;
 }
 
 // TODO: this seems really inefficient (per frag indexing)?