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, 4 insertions, 3 deletions

diff --git a/include/gpu/GrRenderTarget.h b/include/gpu/GrRenderTarget.h
index 4eee7f63ce..9be6e1d8d0 100644
--- a/include/gpu/GrRenderTarget.h
+++ b/include/gpu/GrRenderTarget.h
@@ -33,10 +33,11 @@ public:
     const GrRenderTarget* asRenderTarget() const  override { return this; }
 
     // GrRenderTarget
-    bool isStencilBufferMultisampled() const { return fSampleCnt > 0; }
+    bool isStencilBufferMultisampled() const { return fSampleCnt > 1; }
 
     GrFSAAType fsaaType() const {
-        if (!fSampleCnt) {
+        SkASSERT(fSampleCnt >= 1);
+        if (fSampleCnt <= 1) {
             SkASSERT(!(fFlags & GrRenderTargetFlags::kMixedSampled));
             return GrFSAAType::kNone;
         }
@@ -53,7 +54,7 @@ public:
      * Returns the number of samples/pixel in the color buffer (Zero if non-MSAA or mixed sampled).
      */
     int numColorSamples() const {
-        return GrFSAAType::kMixedSamples == this->fsaaType() ? 0 : fSampleCnt;
+        return GrFSAAType::kMixedSamples == this->fsaaType() ? 1 : fSampleCnt;
     }
 
     /**