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, 3 deletions

diff --git a/src/gpu/GrTexture.cpp b/src/gpu/GrTexture.cpp
index b4cefb0174..dd0631775f 100644
--- a/src/gpu/GrTexture.cpp
+++ b/src/gpu/GrTexture.cpp
@@ -78,7 +78,7 @@ bool GrTexture::StealBackendTexture(sk_sp<GrTexture>&& texture,
 
 void GrTexture::computeScratchKey(GrScratchKey* key) const {
     const GrRenderTarget* rt = this->asRenderTarget();
-    int sampleCount = 0;
+    int sampleCount = 1;
     if (rt) {
         sampleCount = rt->numStencilSamples();
     }
@@ -92,8 +92,10 @@ void GrTexturePriv::ComputeScratchKey(GrPixelConfig config, int width, int heigh
                                       GrMipMapped mipMapped, GrScratchKey* key) {
     static const GrScratchKey::ResourceType kType = GrScratchKey::GenerateResourceType();
     uint32_t flags = isRenderTarget;
-
-    SkASSERT(0 == sampleCnt || isRenderTarget);
+    SkASSERT(width > 0);
+    SkASSERT(height > 0);
+    SkASSERT(sampleCnt > 0);
+    SkASSERT(1 == sampleCnt || isRenderTarget);
 
     // make sure desc.fConfig fits in 5 bits
     SkASSERT(sk_float_log2(kLast_GrPixelConfig) <= 5);