[oden] Circles work

src/circle_shader.wgsl

@@ -31,7 +31,7 @@ struct VertexOutput {
   // The circle's coordinate system goes from (-1,-1) to (1,1) but by
   // convention we provide ourselves texture coordinates that go from (0,0)
   // to (1,1).
-  out.tex_coords = mix(vec2f(-1.0, -1.0), vec2f(1.0, 1.0), vertex.tex_coords);
+  out.tex_coords = (vertex.tex_coords * vec2f(2.0,2.0)) - vec2f(1.0,1.0);
 
   // Compute the squared radius of the inner circle, so we don't do it
   // per-pixel.
@@ -65,7 +65,7 @@ struct VertexOutput {
   } else if (tc2.x + tc2.y <= 1.0) {
      return in.stroke_color;
   } else {
-    return vec4<f32>(0.0, 0.0, 0.0, 1.0);
+    return vec4<f32>(0.0, 0.0, 0.0, 0.0);
   }
 }
 
@@ -76,7 +76,7 @@ struct VertexOutput {
 struct ScreenUniform {
   resolution : vec2f,
 };
-@group(1) @binding(0) // 1.
+@group(0) @binding(0) // 1.
     var<uniform> screen : ScreenUniform;
 
 const RES = vec2f(320.0, 240.0); // The logical resolution of the screen.