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, 2 insertions, 2 deletions

diff --git a/src/gpu/GrSurfaceProxy.cpp b/src/gpu/GrSurfaceProxy.cpp
index 64c47b56b1..4020758259 100644
--- a/src/gpu/GrSurfaceProxy.cpp
+++ b/src/gpu/GrSurfaceProxy.cpp
@@ -26,7 +26,7 @@ static bool is_valid_fully_lazy(const GrSurfaceDesc& desc, SkBackingFit fit) {
     return desc.fWidth <= 0 &&
            desc.fHeight <= 0 &&
            desc.fConfig != kUnknown_GrPixelConfig &&
-           desc.fSampleCnt == 0 &&
+           desc.fSampleCnt == 1 &&
            SkBackingFit::kApprox == fit;
 }
 
@@ -190,7 +190,7 @@ bool GrSurfaceProxy::instantiateImpl(GrResourceProvider* resourceProvider, int s
 void GrSurfaceProxy::computeScratchKey(GrScratchKey* key) const {
     SkASSERT(LazyState::kFully != this->lazyInstantiationState());
     const GrRenderTargetProxy* rtp = this->asRenderTargetProxy();
-    int sampleCount = 0;
+    int sampleCount = 1;
     if (rtp) {
         sampleCount = rtp->numStencilSamples();
     }