Revert "Redefine the meaning of sample counts in GPU backend."

This reverts commit 48825b11ad25c98b9a4884d5cc0edd4e290c4409.

Reason for revert: nanobench

Original change's description:
> 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>

TBR=egdaniel@google.com,bsalomon@google.com

Change-Id: Ic257619a8a5ee9ac15419ecf10259e42daed7f82
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/102662
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>

6 files changed, 23 insertions, 25 deletions

diff --git a/include/core/SkSurface.h b/include/core/SkSurface.h
index d621fdf062..1f2c4b7f07 100644
--- a/include/core/SkSurface.h
+++ b/include/core/SkSurface.h
@@ -90,7 +90,7 @@ public:
     /**
      *  Used to wrap a pre-existing backend 3D API texture as a SkSurface. Skia will not assume
      *  ownership of the texture and the client must ensure the texture is valid for the lifetime
-     *  of the SkSurface. If sampleCnt > 1, then we will create an intermediate mssa surface which
+     *  of the SkSurface. If sampleCnt > 0, then we will create an intermediate mssa surface which
      *  we will use for rendering. We then resolve into the passed in texture.
      */
     static sk_sp<SkSurface> MakeFromBackendTexture(GrContext* context,
@@ -102,13 +102,13 @@ public:
     /**
      *  Used to wrap a pre-existing backend 3D API texture as a SkSurface. Skia will not assume
      *  ownership of the texture and the client must ensure the texture is valid for the lifetime
-     *  of the SkSurface. If sampleCnt > 1, then we will create an intermediate mssa surface which
+     *  of the SkSurface. If sampleCnt > 0, then we will create an intermediate mssa surface which
      *  we will use for rendering. We then resolve into the passed in texture.
      *
      *  The GrBackendTexture must have a valid backend format supplied (GrGLTextureInfo::fFormat,
      *  GrVkImageInfo::fFormat, etc.) in it. The passed in SkColorType informs skia how it should
      *  interpret the backend format supplied by the GrBackendTexture. If the format in the
-     *  GrBackendTexture is not compatible with the sampleCnt, SkColorType, and SkColorSpace we
+     *  GrBackendTexture is not compitable with the sampleCnt, SkColorType, and SkColorSpace we
      *  will return nullptr.
      */
     static sk_sp<SkSurface> MakeFromBackendTexture(GrContext* context,
@@ -128,7 +128,7 @@ public:
      *  The GrBackendRenderTarget must have a valid backend format set (GrGLTextureInfo::fFormat,
      *  GrVkImageInfo::fFormat, etc.) in it. The passed in SkColorType informs skia how it should
      *  interpret the backend format supplied by the GrBackendRenderTarget. If the format in the
-     *  GrBackendRenderTarget is not compatible with the sampleCnt, SkColorType, and SkColorSpace
+     *  GrBackendRenderTarget is not compitable with the sampleCnt, SkColorType, and SkColorSpace
      *  we will return nullptr.
      */
     static sk_sp<SkSurface> MakeFromBackendRenderTarget(GrContext* context,
@@ -162,7 +162,7 @@ public:
      *  The GrBackendTexture must have a valid backend format supplied (GrGLTextureInfo::fFormat,
      *  GrVkImageInfo::fFormat, etc.) in it. The passed in SkColorType informs skia how it should
      *  interpret the backend format supplied by the GrBackendTexture. If the format in the
-     *  GrBackendTexture is not compatible with the sampleCnt, SkColorType, and SkColorSpace we
+     *  GrBackendTexture is not compitable with the sampleCnt, SkColorType, and SkColorSpace we
      *  will return nullptr.
      */
     static sk_sp<SkSurface> MakeFromBackendTextureAsRenderTarget(GrContext* context,
diff --git a/include/gpu/GrCaps.h b/include/gpu/GrCaps.h
index ab77c8877f..f4d6e06280 100644
--- a/include/gpu/GrCaps.h
+++ b/include/gpu/GrCaps.h
@@ -135,9 +135,7 @@ public:
     int maxRasterSamples() const { return fMaxRasterSamples; }
 
     // Find a sample count greater than or equal to the requested count which is supported for a
-    // color buffer of the given config or 0 if no such sample count is supported. If the requested
-    // sample count is 1 then 1 will be returned if non-MSAA rendering is supported, otherwise 0.
-    // For historical reasons requestedCount==0 is handled identically to requestedCount==1.
+    // color buffer of the given config. If MSAA is not support for the config we will return 0.
     virtual int getSampleCount(int requestedCount, GrPixelConfig config) const = 0;
 
     int maxWindowRectangles() const { return fMaxWindowRectangles; }
diff --git a/include/gpu/GrContext.h b/include/gpu/GrContext.h
index 3c79ac74ce..f85efc4940 100644
--- a/include/gpu/GrContext.h
+++ b/include/gpu/GrContext.h
@@ -226,7 +226,7 @@ public:
                                                  int width, int height,
                                                  GrPixelConfig config,
                                                  sk_sp<SkColorSpace> colorSpace,
-                                                 int sampleCnt = 1,
+                                                 int sampleCnt = 0,
                                                  GrMipMapped = GrMipMapped::kNo,
                                                  GrSurfaceOrigin origin = kBottomLeft_GrSurfaceOrigin,
                                                  const SkSurfaceProps* surfaceProps = nullptr,
@@ -242,7 +242,7 @@ public:
                                                  int width, int height,
                                                  GrPixelConfig config,
                                                  sk_sp<SkColorSpace> colorSpace,
-                                                 int sampleCnt = 1,
+                                                 int sampleCnt = 0,
                                                  GrMipMapped = GrMipMapped::kNo,
                                                  GrSurfaceOrigin origin = kBottomLeft_GrSurfaceOrigin,
                                                  const SkSurfaceProps* surfaceProps = nullptr,
diff --git a/include/gpu/GrRenderTarget.h b/include/gpu/GrRenderTarget.h
index 9be6e1d8d0..4eee7f63ce 100644
--- a/include/gpu/GrRenderTarget.h
+++ b/include/gpu/GrRenderTarget.h
@@ -33,11 +33,10 @@ public:
     const GrRenderTarget* asRenderTarget() const  override { return this; }
 
     // GrRenderTarget
-    bool isStencilBufferMultisampled() const { return fSampleCnt > 1; }
+    bool isStencilBufferMultisampled() const { return fSampleCnt > 0; }
 
     GrFSAAType fsaaType() const {
-        SkASSERT(fSampleCnt >= 1);
-        if (fSampleCnt <= 1) {
+        if (!fSampleCnt) {
             SkASSERT(!(fFlags & GrRenderTargetFlags::kMixedSampled));
             return GrFSAAType::kNone;
         }
@@ -54,7 +53,7 @@ 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() ? 1 : fSampleCnt;
+        return GrFSAAType::kMixedSamples == this->fsaaType() ? 0 : fSampleCnt;
     }
 
     /**
diff --git a/include/gpu/GrTypes.h b/include/gpu/GrTypes.h
index ab21fba732..3081543aac 100644
--- a/include/gpu/GrTypes.h
+++ b/include/gpu/GrTypes.h
@@ -402,12 +402,13 @@ struct GrMipLevel {
  */
 struct GrSurfaceDesc {
     GrSurfaceDesc()
-            : fFlags(kNone_GrSurfaceFlags)
-            , fOrigin(kTopLeft_GrSurfaceOrigin)
-            , fWidth(0)
-            , fHeight(0)
-            , fConfig(kUnknown_GrPixelConfig)
-            , fSampleCnt(1) {}
+        : fFlags(kNone_GrSurfaceFlags)
+        , fOrigin(kTopLeft_GrSurfaceOrigin)
+        , fWidth(0)
+        , fHeight(0)
+        , fConfig(kUnknown_GrPixelConfig)
+        , fSampleCnt(0) {
+    }
 
     GrSurfaceFlags         fFlags;  //!< bitfield of TextureFlags
     GrSurfaceOrigin        fOrigin; //!< origin of the texture
@@ -421,11 +422,11 @@ struct GrSurfaceDesc {
     GrPixelConfig          fConfig;
 
     /**
-     * The number of samples per pixel. Zero is treated equivalently to 1. This only
+     * The number of samples per pixel or 0 to disable full scene AA. This only
      * applies if the kRenderTarget_GrSurfaceFlag is set. The actual number
      * of samples may not exactly match the request. The request will be rounded
-     * up to the next supported sample count. A value larger than the largest
-     * supported sample count will fail.
+     * up to the next supported sample count, or down if it is larger than the
+     * max supported count.
      */
     int                    fSampleCnt;
 };
diff --git a/include/private/GrRenderTargetProxy.h b/include/private/GrRenderTargetProxy.h
index 1d5d8042ce..1cd3d5d1a2 100644
--- a/include/private/GrRenderTargetProxy.h
+++ b/include/private/GrRenderTargetProxy.h
@@ -26,7 +26,7 @@ public:
     bool instantiate(GrResourceProvider*) override;
 
     GrFSAAType fsaaType() const {
-        if (fSampleCnt <= 1) {
+        if (!fSampleCnt) {
             SkASSERT(!(fRenderTargetFlags & GrRenderTargetFlags::kMixedSampled));
             return GrFSAAType::kNone;
         }
@@ -50,7 +50,7 @@ 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() ? 1 : fSampleCnt;
+        return GrFSAAType::kMixedSamples == this->fsaaType() ? 0 : fSampleCnt;
     }
 
     int maxWindowRectangles(const GrCaps& caps) const;