Fix BGRA/RGBA readback conversions on mac

Reading back from a BGRA framebuffer as RGBA or vis-versa is slow on mac. On my early 2013 MBP, we see a 40% regression when using
the discrete GPU or a 13% regression on integrated.

This change adds a workaround which causes Mac to use the existing Mesa path and prefer readback from the same format as the
framebuffer.

BUG=581311
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1786813002

Review URL: https://codereview.chromium.org/1786813002

3 files changed, 18 insertions, 1 deletions

diff --git a/src/gpu/gl/GrGLCaps.cpp b/src/gpu/gl/GrGLCaps.cpp
index dfcde60d45..40885359fb 100644
--- a/src/gpu/gl/GrGLCaps.cpp
+++ b/src/gpu/gl/GrGLCaps.cpp
@@ -51,6 +51,7 @@ GrGLCaps::GrGLCaps(const GrContextOptions& contextOptions,
     fRGBA8888PixelsOpsAreSlow = false;
     fPartialFBOReadIsSlow = false;
     fMipMapLevelAndLodControlSupport = false;
+    fRGBAToBGRAReadbackConversionsAreSlow = false;
 
     fBlitFramebufferSupport = kNone_BlitFramebufferSupport;
 
@@ -253,6 +254,16 @@ void GrGLCaps::init(const GrContextOptions& contextOptions,
     fPartialFBOReadIsSlow = isANGLE;
 #endif
 
+    bool isMESA = kMesa_GrGLDriver == ctxInfo.driver();
+    bool isMAC = false;
+#ifdef SK_BUILD_FOR_MAC
+    isMAC = true;
+#endif
+
+    // Both mesa and mac have reduced performance if reading back an RGBA framebuffer as BGRA or
+    // vis-versa.
+    fRGBAToBGRAReadbackConversionsAreSlow = isMESA || isMAC;
+
     /**************************************************************************
     * GrShaderCaps fields
     **************************************************************************/
@@ -1077,6 +1088,8 @@ SkString GrGLCaps::dump() const {
     r.appendf("Bind uniform location support: %s\n", (fBindUniformLocationSupport ? "YES" : "NO"));
     r.appendf("Rectangle texture support: %s\n", (fRectangleTextureSupport? "YES" : "NO"));
     r.appendf("Texture swizzle support: %s\n", (fTextureSwizzleSupport ? "YES" : "NO"));
+    r.appendf("BGRA to RGBA readback conversions are slow: %s\n", 
+              (fRGBAToBGRAReadbackConversionsAreSlow ? "YES" : "NO"));
 
     r.append("Configs\n-------\n");
     for (int i = 0; i < kGrPixelConfigCnt; ++i) {
diff --git a/src/gpu/gl/GrGLCaps.h b/src/gpu/gl/GrGLCaps.h
index cf162914de..376610d8b0 100644
--- a/src/gpu/gl/GrGLCaps.h
+++ b/src/gpu/gl/GrGLCaps.h
@@ -345,6 +345,9 @@ public:
 
     bool rgba8888PixelsOpsAreSlow() const { return fRGBA8888PixelsOpsAreSlow; }
     bool partialFBOReadIsSlow() const { return fPartialFBOReadIsSlow; }
+    bool rgbaToBgraReadbackConversionsAreSlow() const {
+        return fRGBAToBGRAReadbackConversionsAreSlow;
+    }
 
     const GrGLSLCaps* glslCaps() const { return reinterpret_cast<GrGLSLCaps*>(fShaderCaps.get()); }
 
@@ -413,6 +416,7 @@ private:
     bool fRectangleTextureSupport : 1;
     bool fTextureSwizzleSupport : 1;
     bool fMipMapLevelAndLodControlSupport : 1;
+    bool fRGBAToBGRAReadbackConversionsAreSlow : 1;
 
     BlitFramebufferSupport fBlitFramebufferSupport;
 
diff --git a/src/gpu/gl/GrGLGpu.cpp b/src/gpu/gl/GrGLGpu.cpp
index 443c55c234..3e8f507b4a 100644
--- a/src/gpu/gl/GrGLGpu.cpp
+++ b/src/gpu/gl/GrGLGpu.cpp
@@ -2560,7 +2560,7 @@ bool GrGLGpu::onGetReadPixelsInfo(GrSurface* srcSurface, int width, int height,
         tempDrawInfo->fSwizzle = GrSwizzle::BGRA();
         tempDrawInfo->fReadConfig = kBGRA_8888_GrPixelConfig;
         ElevateDrawPreference(drawPreference, kGpuPrefersDraw_DrawPreference);
-    } else if (kMesa_GrGLDriver == this->glContext().driver() &&
+    } else if (this->glCaps().rgbaToBgraReadbackConversionsAreSlow() &&
                GrBytesPerPixel(readConfig) == 4 &&
                GrPixelConfigSwapRAndB(readConfig) == srcConfig &&
                this->readPixelsSupported(srcSurface, srcConfig)) {