Update the postprocessing shader and vertex array for the Metal changes.

Closes #201.

renderer/src/gpu/renderer.rs

@@ -654,7 +654,7 @@ where
             }
         }
 
-        self.device.draw_arrays(4, &RenderState {
+        self.device.draw_elements(6, &RenderState {
             target: &self.dest_render_target(),
             program: &self.postprocess_program.program,
             vertex_array: &self.postprocess_vertex_array.vertex_array,
@@ -1451,7 +1451,7 @@ where
         device.configure_vertex_attr(&vertex_array, &position_attr, &VertexAttrDescriptor {
             size: 2,
             class: VertexAttrClass::Int,
-            attr_type: VertexAttrType::U16,
+            attr_type: VertexAttrType::I16,
             stride: 4,
             offset: 0,
             divisor: 0,

resources/shaders/gl3/post.vs.glsl

@@ -19,7 +19,13 @@ in ivec2 aPosition;
 out vec2 vTexCoord;
 
 void main(){
-    vTexCoord = vec2(aPosition);
-    gl_Position = vec4(vec2(aPosition)* 2.0 - 1.0, 0.0, 1.0);
+    vec2 position = vec2(aPosition);
+    vTexCoord = position;
+
+
+
+
+
+    gl_Position = vec4(vec2(position)* 2.0 - 1.0, 0.0, 1.0);
 }
 

resources/shaders/metal/post.vs.metal

@@ -18,8 +18,10 @@ struct main0_in
 vertex main0_out main0(main0_in in [[stage_in]])
 {
     main0_out out = {};
-    out.vTexCoord = float2(in.aPosition);
-    out.gl_Position = float4((float2(in.aPosition) * 2.0) - float2(1.0), 0.0, 1.0);
+    float2 position = float2(in.aPosition);
+    out.vTexCoord = position;
+    position.y = 1.0 - position.y;
+    out.gl_Position = float4((float2(position) * 2.0) - float2(1.0), 0.0, 1.0);
     return out;
 }
 

shaders/post.vs.glsl

@@ -17,6 +17,12 @@ in ivec2 aPosition;
 out vec2 vTexCoord;
 
 void main() {
-    vTexCoord = vec2(aPosition);
-    gl_Position = vec4(vec2(aPosition) * 2.0 - 1.0, 0.0, 1.0);
+    vec2 position = vec2(aPosition);
+    vTexCoord = position;
+
+#ifdef PF_ORIGIN_UPPER_LEFT
+    // FIXME(pcwalton): This is wrong.
+    position.y = 1.0 - position.y;
+#endif
+    gl_Position = vec4(vec2(position) * 2.0 - 1.0, 0.0, 1.0);
 }