Redefine the meaning of sample counts in GPU backend.

Old: 0  -> nonMSAA
     1+ -> MSAA

New:
     0  -> error/unsupported
     1  -> nonMSAA
     2+ -> MSAA

We still allow 0 to mean nonMSAA in three sets of public APIs for backwards compatibility:

1) SkSurface factories
2) GrBackendRenderTarget constructors
3) GrCaps::getSampleCnt()'s requestedCount parameter

However, we immediately clamp to 1 and treat 0 as invalid/non-renderable internally.

This also changes the behavior when using a large sample count. We now fail in that case rather than using the largest sample available sample count. GrCaps::getSampleCount() will return 0 in this case.


Bug: skia:
Change-Id: Ida22c6b22c1365e563c9046b611e88bf5eb3ff33
Reviewed-on: https://skia-review.googlesource.com/101560
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/tools/sk_app/android/GLWindowContext_android.cpp b/tools/sk_app/android/GLWindowContext_android.cpp
index acdb587230..5111114115 100644
--- a/tools/sk_app/android/GLWindowContext_android.cpp
+++ b/tools/sk_app/android/GLWindowContext_android.cpp
@@ -70,6 +70,8 @@ sk_sp<const GrGLInterface> GLWindowContext_android::onInitializeContext() {
     SkAssertResult(eglBindAPI(EGL_OPENGL_ES_API));
 
     EGLint numConfigs = 0;
+    EGLint eglSampleCnt = fDisplayParams.fMSAASampleCount > 1 ? fDisplayParams.fMSAASampleCount > 1
+                                                              : 0;
     const EGLint configAttribs[] = {
         EGL_SURFACE_TYPE, EGL_PBUFFER_BIT,
         EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
@@ -78,8 +80,8 @@ sk_sp<const GrGLInterface> GLWindowContext_android::onInitializeContext() {
         EGL_BLUE_SIZE, 8,
         EGL_ALPHA_SIZE, 8,
         EGL_STENCIL_SIZE, 8,
-        EGL_SAMPLE_BUFFERS, fDisplayParams.fMSAASampleCount ? 1 : 0,
-        EGL_SAMPLES, fDisplayParams.fMSAASampleCount,
+        EGL_SAMPLE_BUFFERS, eglSampleCnt ? 1 : 0,
+        EGL_SAMPLES, eglSampleCnt,
         EGL_NONE
     };
 
@@ -131,6 +133,7 @@ sk_sp<const GrGLInterface> GLWindowContext_android::onInitializeContext() {
 
     eglGetConfigAttrib(fDisplay, surfaceConfig, EGL_STENCIL_SIZE, &fStencilBits);
     eglGetConfigAttrib(fDisplay, surfaceConfig, EGL_SAMPLES, &fSampleCount);
+    fSampleCount = SkTMax(fSampleCount, 1);
 
     return GrGLMakeNativeInterface();
 }