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, 4 deletions

diff --git a/tools/sk_app/GLWindowContext.cpp b/tools/sk_app/GLWindowContext.cpp
index 9ef5141fee..9d042cf19e 100644
--- a/tools/sk_app/GLWindowContext.cpp
+++ b/tools/sk_app/GLWindowContext.cpp
@@ -24,9 +24,7 @@ GLWindowContext::GLWindowContext(const DisplayParams& params)
     : WindowContext(params)
     , fBackendContext(nullptr)
     , fSurface(nullptr) {
-    fDisplayParams.fMSAASampleCount = fDisplayParams.fMSAASampleCount ?
-                                      GrNextPow2(fDisplayParams.fMSAASampleCount) :
-                                      0;
+    fDisplayParams.fMSAASampleCount = GrNextPow2(fDisplayParams.fMSAASampleCount);
 }
 
 void GLWindowContext::initializeContext() {
@@ -34,7 +32,7 @@ void GLWindowContext::initializeContext() {
 
     fBackendContext = this->onInitializeContext();
     fContext = GrContext::MakeGL(fBackendContext, fDisplayParams.fGrContextOptions);
-    if (!fContext && fDisplayParams.fMSAASampleCount) {
+    if (!fContext && fDisplayParams.fMSAASampleCount > 1) {
         fDisplayParams.fMSAASampleCount /= 2;
         this->initializeContext();
         return;