[Metal] update depth camera and selection buffer shaders to match #446 (

#498)

- Add new param colorTexResolution to the selection buffer shader
- Implement the Metal equivalent of texelFetch in the shaders

Signed-off-by: Rhys Mainwaring <[email protected]>

ogre2/src/media/materials/programs/Metal/depth_camera_final_fs.metal

@@ -49,9 +49,10 @@ fragment float4 main_metal
   // values close to 0 get rounded to 0)
   //
   // See https://github.com/ignitionrobotics/ign-rendering/issues/332
-  // float4 p = texelFetch(inputTexture, int2(inPs.uv0 * params.texResolution.xy), 0);
-  // TODO - establish Metal equivalent - use standard sampler as interim approx.
-  float4 p = inputTexture.sample(inputSampler, inPs.uv0);
+  // Either: Metal equivalent of texelFetch
+  float4 p = inputTexture.read(uint2(inPs.uv0 * params.texResolution.xy), 0);
+  // Or: Use standard sampler
+  // float4 p = inputTexture.sample(inputSampler, inPs.uv0);
 
   float3 point = p.xyz;
 

ogre2/src/media/materials/programs/Metal/selection_buffer_fs.metal

@@ -29,6 +29,7 @@ struct Params
   float2  projectionParams;
   float   far;
   float   inf;
+  float4  colorTexResolution;
 };
 
 float packFloat(float4 color)
@@ -66,7 +67,11 @@ fragment float4 main_metal
     point = float3(p.inf);
 
   // color
-  float4 color = colorTexture.sample(colorSampler, inPs.uv0);
+  // Either: Metal equivalent of texelFetch
+  float4 color = colorTexture.read(
+      uint2(inPs.uv0 * p.colorTexResolution.xy), 0);
+  // Or: Use standard sampler
+  // float4 color = colorTexture.sample(colorSampler, inPs.uv0);
 
   float rgba = packFloat(color);