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>

3 files changed, 10 insertions, 8 deletions

diff --git a/tools/sk_app/unix/GLWindowContext_unix.cpp b/tools/sk_app/unix/GLWindowContext_unix.cpp
index 25ec95cdd6..3a3a4b16d4 100644
--- a/tools/sk_app/unix/GLWindowContext_unix.cpp
+++ b/tools/sk_app/unix/GLWindowContext_unix.cpp
@@ -99,6 +99,7 @@ sk_sp<const GrGLInterface> GLWindowContext_xlib::onInitializeContext() {
 
     glXGetConfig(fDisplay, fVisualInfo, GLX_STENCIL_SIZE, &fStencilBits);
     glXGetConfig(fDisplay, fVisualInfo, GLX_SAMPLES_ARB, &fSampleCount);
+    fSampleCount = SkTMax(fSampleCount, 1);
 
     XWindow root;
     int x, y;
diff --git a/tools/sk_app/unix/Window_unix.cpp b/tools/sk_app/unix/Window_unix.cpp
index f5ca5ee073..745b4dd3fb 100644
--- a/tools/sk_app/unix/Window_unix.cpp
+++ b/tools/sk_app/unix/Window_unix.cpp
@@ -72,7 +72,7 @@ bool Window_unix::initWindow(Display* display) {
         None
     };
     SkASSERT(nullptr == fVisualInfo);
-    if (fRequestedDisplayParams.fMSAASampleCount > 0) {
+    if (fRequestedDisplayParams.fMSAASampleCount > 1) {
         static const GLint kChooseFBConifgAttCnt = SK_ARRAY_COUNT(kChooseFBConfigAtt);
         GLint msaaChooseFBConfigAtt[kChooseFBConifgAttCnt + 4];
         memcpy(msaaChooseFBConfigAtt, kChooseFBConfigAtt, sizeof(kChooseFBConfigAtt));
diff --git a/tools/sk_app/unix/Window_unix.h b/tools/sk_app/unix/Window_unix.h
index b59f502eb9..62a2795098 100644
--- a/tools/sk_app/unix/Window_unix.h
+++ b/tools/sk_app/unix/Window_unix.h
@@ -20,13 +20,14 @@ namespace sk_app {
 
 class Window_unix : public Window {
 public:
-    Window_unix() : Window()
-                  , fDisplay(nullptr)
-                  , fWindow(0)
-                  , fGC(nullptr)
-                  , fFBConfig(nullptr)
-                  , fVisualInfo(nullptr)
-                  , fMSAASampleCount(0) {}
+    Window_unix()
+            : Window()
+            , fDisplay(nullptr)
+            , fWindow(0)
+            , fGC(nullptr)
+            , fFBConfig(nullptr)
+            , fVisualInfo(nullptr)
+            , fMSAASampleCount(1) {}
     ~Window_unix() override { this->closeWindow(); }
 
     bool initWindow(Display* display);