Refactoring of GPU NormalMap handling out into its own class.

The purpose of this change is to refactor the handling of normal maps out of SkLightingShader, laying the groundwork to eventually allow for multiple normal sources.

What this CL includes:

- Created a new 'NormalMapFP', out of the existing normal map reading behavior in LightingFP.

- Encapsulates this new fragment processor on a new class NormalMapSource.

- Created a NormalSource abstraction that will interface with SkLightingShader.

- Adapted SkLightingShader to use the normals from its NormalSource field ON THE GPU SIDE. No changes done to the CPU side yet.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2043393002

Committed: https://skia.googlesource.com/skia/+/87b0dd00cf9409c5fc990f5d0bb7c0df837f08da
Review-Url: https://codereview.chromium.org/2043393002

1 files changed, 52 insertions, 0 deletions

diff --git a/src/core/SkLightingShader.h b/src/core/SkLightingShader.h
index f25b30342a..6301eeeea1 100644
--- a/src/core/SkLightingShader.h
+++ b/src/core/SkLightingShader.h
@@ -16,6 +16,58 @@ class SkMatrix;
 
 class SK_API SkLightingShader {
 public:
+    /** Abstract class that generates or reads in normals for use by SkLightingShader. Currently
+        implements the GPU side only. Not to be used as part of the API yet. Used internally by
+        SkLightingShader.
+    */
+    class NormalSource : public SkFlattenable {
+    public:
+        virtual ~NormalSource();
+
+#if SK_SUPPORT_GPU
+
+        /** Returns a fragment processor that takes no input and outputs a normal (already rotated)
+            as its output color. To be used as a child fragment processor.
+        */
+        virtual sk_sp<GrFragmentProcessor> asFragmentProcessor(
+                GrContext* context,
+                const SkMatrix& viewM,
+                const SkMatrix* localMatrix,
+                SkFilterQuality filterQuality,
+                SkSourceGammaTreatment gammaTreatment) const = 0;
+#endif
+
+        SK_DEFINE_FLATTENABLE_TYPE(NormalSource)
+    };
+
+    /** Returns a normal source that provides normals sourced from the the normal map argument.
+        Not to be used as part of the API yet. Used internally by SkLightingShader.
+
+        @param  normal                the normal map
+        @param  invNormRotation       rotation applied to the normal map's normals
+        @param  normLocalM            the local matrix for the normal map
+
+        nullptr will be returned if
+            'normal' is empty
+            'normal' too big (> 65535 on either side)
+
+        The normal map is currently assumed to be an 8888 image where the normal at a texel
+        is retrieved by:
+            N.x = R-127;
+            N.y = G-127;
+            N.z = B-127;
+            N.normalize();
+        The +Z axis is thus encoded in RGB as (127, 127, 255) while the -Z axis is
+        (127, 127, 0).
+    */
+    class NormalMapSource {
+    public:
+        static sk_sp<NormalSource> Make(const SkBitmap& normal, const SkVector& invNormRotation,
+                                        const SkMatrix* normLocalM);
+
+        SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
+    };
+
     /** Returns a shader that lights the diffuse and normal maps with a set of lights.
 
         It returns a shader with a reference count of 1.