Metal: draw 1 triangle instead of 2 for fullscreen shaders.

scripts/code_generation_hashes/Metal_default_shaders.json

 {
   "src/libANGLE/renderer/metal/shaders/blit.metal":
-    "86cad2bdbbed1fe7ec94f4ce01ede0c1",
+    "9281aba529ceb4ed5131b7f9c0515362",
   "src/libANGLE/renderer/metal/shaders/clear.metal":
     "1c231afc6100433a79fce49046aa5965",
   "src/libANGLE/renderer/metal/shaders/common.h":
-    "d44903e10552301d7ec89c1a0e6e0862",
+    "569171e345ef36dd6a3b12aeebfae4a6",
   "src/libANGLE/renderer/metal/shaders/compiled/mtl_default_shaders.inc":
-    "ae02216e4b3588d28b0e87a54deddabb",
+    "c42c37285c375de9a065b925ed54aebd",
   "src/libANGLE/renderer/metal/shaders/gen_indices.metal":
     "002511e2b980a7fca7e80cbda6a82712",
   "src/libANGLE/renderer/metal/shaders/gen_mtl_internal_shaders.py":
@@ -14,5 +14,5 @@
   "src/libANGLE/renderer/metal/shaders/master_source.metal":
     "fbe6f4bfb49a48ae87791a4cff5fab0a",
   "src/libANGLE/renderer/metal/shaders/mtl_default_shaders_src_autogen.inc":
-    "492ddcfd51acfc95d02de2658cf999cd"
+    "8a94beb0d979f472d71686b6f95b624f"
 }
\ No newline at end of file

src/libANGLE/renderer/metal/mtl_render_utils.mm

@@ -39,14 +39,13 @@ struct ClearParamsUniform
 
 struct BlitParamsUniform
 {
-    // 0: lower left, 1: lower right, 2: upper left, 3: upper right
-    float srcTexCoords[4][2];
+    // 0: lower left, 1: lower right, 2: upper left
+    float srcTexCoords[3][2];
     int srcLevel         = 0;
     uint8_t srcLuminance = 0;  // source texture is luminance texture
     uint8_t dstFlipY     = 0;
     uint8_t dstLuminance = 0;  // dest texture is luminace
-    uint8_t padding1;
-    float padding2[2];
+    uint8_t padding;
 };
 
 struct IndexConversionUniform
@@ -229,8 +228,8 @@ void RenderUtils::clearWithDraw(const gl::Context *context,
 
     setupClearWithDraw(context, cmdEncoder, overridedParams);
 
-    // Draw the screen aligned quad
-    cmdEncoder->draw(MTLPrimitiveTypeTriangle, 0, 6);
+    // Draw the screen aligned triangle
+    cmdEncoder->draw(MTLPrimitiveTypeTriangle, 0, 3);
 
     // Invalidate current context's state
     auto contextMtl = GetImpl(context);
@@ -247,8 +246,8 @@ void RenderUtils::blitWithDraw(const gl::Context *context,
     }
     setupBlitWithDraw(context, cmdEncoder, params);
 
-    // Draw the screen aligned quad
-    cmdEncoder->draw(MTLPrimitiveTypeTriangle, 0, 6);
+    // Draw the screen aligned triangle
+    cmdEncoder->draw(MTLPrimitiveTypeTriangle, 0, 3);
 
     // Invalidate current context's state
     ContextMtl *contextMtl = GetImpl(context);
@@ -474,26 +473,24 @@ void RenderUtils::setupBlitWithDrawUniformData(RenderCommandEncoder *cmdEncoder,
         std::swap(y0, y1);
     }
 
-    float u0 = (float)x0 / srcWidth;
-    float u1 = (float)x1 / srcWidth;
-    float v0 = (float)y0 / srcHeight;
-    float v1 = (float)y1 / srcHeight;
+    float u0 = static_cast<float>(x0) / srcWidth;
+    float u1 = static_cast<float>(x1) / srcWidth;
+    float v0 = static_cast<float>(y0) / srcHeight;
+    float v1 = static_cast<float>(y1) / srcHeight;
+    float du = static_cast<float>(x1 - x0) / srcWidth;
+    float dv = static_cast<float>(y1 - y0) / srcHeight;
 
     // lower left
     uniformParams.srcTexCoords[0][0] = u0;
     uniformParams.srcTexCoords[0][1] = v0;
 
     // lower right
-    uniformParams.srcTexCoords[1][0] = u1;
+    uniformParams.srcTexCoords[1][0] = u1 + du;
     uniformParams.srcTexCoords[1][1] = v0;
 
     // upper left
     uniformParams.srcTexCoords[2][0] = u0;
-    uniformParams.srcTexCoords[2][1] = v1;
-
-    // upper right
-    uniformParams.srcTexCoords[3][0] = u1;
-    uniformParams.srcTexCoords[3][1] = v1;
+    uniformParams.srcTexCoords[2][1] = v1 + dv;
 
     cmdEncoder->setVertexData(uniformParams, 0);
     cmdEncoder->setFragmentData(uniformParams, 0);

src/libANGLE/renderer/metal/shaders/blit.metal

@@ -10,8 +10,8 @@
 
 struct BlitParams
 {
-    // 0: lower left, 1: lower right, 2: upper left, 3: upper right
-    float2 srcTexCoords[4];
+    // 0: lower left, 1: lower right, 2: upper left
+    float2 srcTexCoords[3];
     int srcLevel;
     bool srcLuminance; // source texture is luminance texture
     bool dstFlipViewportY;
@@ -28,8 +28,8 @@ vertex BlitVSOut blitVS(unsigned int vid [[ vertex_id ]],
                          constant BlitParams &options [[buffer(0)]])
 {
     BlitVSOut output;
-    output.position = float4(gCorners[vid], 0.0, 1.0);
-    output.texCoords = options.srcTexCoords[gTexcoordsIndices[vid]];
+    output.position  = float4(gCorners[vid], 0.0, 1.0);
+    output.texCoords = options.srcTexCoords[vid];
 
     if (!options.dstFlipViewportY)
     {

src/libANGLE/renderer/metal/shaders/common.h

@@ -21,15 +21,8 @@
 
 using namespace metal;
 
-// Full screen quad's vertices
-constant float2 gCorners[6] = {
-    float2(-1.0f, 1.0f), float2(1.0f, -1.0f), float2(-1.0f, -1.0f),
-    float2(-1.0f, 1.0f), float2(1.0f, 1.0f),  float2(1.0f, -1.0f),
-};
-
-// Full screen quad's texcoords indices:
-// 0: lower left, 1: lower right, 2: upper left, 3: upper right
-constant int gTexcoordsIndices[6] = {2, 1, 0, 2, 3, 1};
+// Full screen triangle's vertices
+constant float2 gCorners[3] = {float2(-1.0f, -1.0f), float2(3.0f, -1.0f), float2(-1.0f, 3.0f)};
 
 fragment float4 dummyFS()
 {

src/libANGLE/renderer/metal/shaders/mtl_default_shaders_src_autogen.inc

 // GENERATED FILE - DO NOT EDIT.
 // Generated by gen_mtl_internal_shaders.py
 //
-// Copyright 2019 The ANGLE Project Authors. All rights reserved.
+// Copyright 2020 The ANGLE Project Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
@@ -17,7 +17,7 @@ constexpr char default_metallib_src[] = R"(
 # 1 "master_source.metal"
 # 1 "<built-in>" 1
 # 1 "<built-in>" 3
-# 374 "<built-in>" 3
+# 376 "<built-in>" 3
 # 1 "<command line>" 1
 # 1 "<built-in>" 2
 # 1 "master_source.metal" 2
@@ -42,14 +42,7 @@ constexpr char default_metallib_src[] = R"(
 using namespace metal;
 
 
-constant float2 gCorners[6] = {
-    float2(-1.0f, 1.0f), float2(1.0f, -1.0f), float2(-1.0f, -1.0f),
-    float2(-1.0f, 1.0f), float2(1.0f, 1.0f), float2(1.0f, -1.0f),
-};
-
-
-
-constant int gTexcoordsIndices[6] = {2, 1, 0, 2, 3, 1};
+constant float2 gCorners[3] = {float2(-1.0f, -1.0f), float2(3.0f, -1.0f), float2(-1.0f, 3.0f)};
 
 fragment float4 dummyFS()
 {
@@ -79,7 +72,7 @@ fragment float4 clearFS(constant ClearParams &clearParams [[buffer(0)]])
 struct BlitParams
 {
 
-    float2 srcTexCoords[4];
+    float2 srcTexCoords[3];
     int srcLevel;
     bool srcLuminance;
     bool dstFlipViewportY;
@@ -97,7 +90,7 @@ vertex BlitVSOut blitVS(unsigned int vid [[ vertex_id ]],
 {
     BlitVSOut output;
     output.position = float4(gCorners[vid], 0.0, 1.0);
-    output.texCoords = options.srcTexCoords[gTexcoordsIndices[vid]];
+    output.texCoords = options.srcTexCoords[vid];
 
     if (!options.dstFlipViewportY)
     {