Fix some GPU image filter code to preserve precision and color space

On the pure-GPU path, we just have an SkSpecialImage (that's definitely
texture backed), and we need a renderable config for the draw context we
make. Added a helper function to pick - this is basically the high
precision analog of what we were doing before (always using 8888).

The assert that I added catches many other problems in image filter code,
but those fixes are coming in subsequent CLs.

12 GMs render correctly (or more correctly) in gpusrgb and gpuf16
configs. In most cases, they were drawing previously nothing.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2359443003

Review-Url: https://codereview.chromium.org/2359443003

3 files changed, 20 insertions, 0 deletions

diff --git a/src/gpu/GrDrawingManager.cpp b/src/gpu/GrDrawingManager.cpp
index 606a9abd6e..9dd5613f21 100644
--- a/src/gpu/GrDrawingManager.cpp
+++ b/src/gpu/GrDrawingManager.cpp
@@ -222,6 +222,8 @@ sk_sp<GrDrawContext> GrDrawingManager::makeDrawContext(sk_sp<GrRenderTarget> rt,
     // by, including internal usage. We allow a null color space here, for read/write pixels and
     // other special code paths. If a color space is provided, though, enforce all other rules.
     if (colorSpace && !SkSurface_Gpu::Valid(fContext, rt->config(), colorSpace.get())) {
+        // SRGBTODO: Enable this assert once image filters are propagating color type and space
+//        SkDEBUGFAIL("Invalid config and colorspace combination");
         return nullptr;
     }
 
diff --git a/src/gpu/SkGr.cpp b/src/gpu/SkGr.cpp
index c8839f3f1a..9ee8722afa 100644
--- a/src/gpu/SkGr.cpp
+++ b/src/gpu/SkGr.cpp
@@ -508,6 +508,19 @@ bool GrPixelConfigToColorType(GrPixelConfig config, SkColorType* ctOut) {
     return true;
 }
 
+GrPixelConfig GrRenderableConfigForColorSpace(SkColorSpace* colorSpace) {
+    if (!colorSpace) {
+        return kRGBA_8888_GrPixelConfig;
+    } else if (colorSpace->gammaIsLinear()) {
+        return kRGBA_half_GrPixelConfig;
+    } else if (colorSpace->gammaCloseToSRGB()) {
+        return kSRGBA_8888_GrPixelConfig;
+    } else {
+        SkDEBUGFAIL("No renderable config exists for color space with strange gamma");
+        return kUnknown_GrPixelConfig;
+    }
+}
+
 ////////////////////////////////////////////////////////////////////////////////////////////////
 
 static inline bool blend_requires_shader(const SkXfermode::Mode mode, bool primitiveIsSrc) {
diff --git a/src/gpu/SkGrPriv.h b/src/gpu/SkGrPriv.h
index 26dc4aaa86..c1069d1a20 100644
--- a/src/gpu/SkGrPriv.h
+++ b/src/gpu/SkGrPriv.h
@@ -105,6 +105,11 @@ GrSurfaceDesc GrImageInfoToSurfaceDesc(const SkImageInfo&, const GrCaps&);
 
 bool GrPixelConfigToColorType(GrPixelConfig, SkColorType*);
 
+/** When image filter code needs to construct a draw context to do intermediate rendering, we need
+    a renderable pixel config. The source (SkSpecialImage) may not be in a renderable format, but
+    we want to preserve the color space of that source. This picks an appropriate format to use. */
+GrPixelConfig GrRenderableConfigForColorSpace(SkColorSpace*);
+
 /**
  *  If the compressed data in the SkData is supported (as a texture format, this returns
  *  the pixel-config that should be used, and sets outStartOfDataToUpload to the ptr into