Make GPU coord transforms automatic

include/gpu/GrCoordTransform.h

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrCoordTransform_DEFINED
+#define GrCoordTransform_DEFINED
+
+#include "GrEffect.h"
+#include "SkMatrix.h"
+#include "GrTexture.h"
+#include "GrTypes.h"
+
+/**
+ * Coordinates available to GrEffect subclasses for requesting transformations. Transformed
+ * coordinates are made available in the the portion of fragment shader emitted by the effect.
+ */
+enum GrCoordSet {
+    /**
+     * The user-space coordinates that map to the fragment being rendered. These coords account for
+     * any change of coordinate system done on the CPU by GrContext before rendering, and also are
+     * correct for draws that take explicit local coords rather than inferring them from the
+     * primitive's positions (e.g. drawVertices). These are usually the coords a GrEffect wants.
+     */
+    kLocal_GrCoordSet,
+
+    /**
+     * The actual vertex position. Note that GrContext may not draw using the original view matrix
+     * specified by the caller, as it may have transformed vertices into another space. These are
+     * usually not the coordinates a GrEffect wants.
+     */
+    kPosition_GrCoordSet
+};
+
+/**
+ * A class representing a linear transformation from one of the built-in coordinate sets (local or
+ * position). GrEffects just define these transformations, and the framework does the rest of the
+ * work to make the transformed coordinates available in their fragment shader.
+ */
+class GrCoordTransform : public SkNoncopyable {
+public:
+    GrCoordTransform() {}
+
+    /**
+     * Create a transformation that maps [0, 1] to a texture's boundaries.
+     */
+    GrCoordTransform(GrCoordSet sourceCoords, const GrTexture* texture) {
+        this->reset(sourceCoords, texture);
+    }
+
+    /**
+     * Create a transformation from a matrix. The optional texture parameter is used to infer if the
+     * framework should internally do a y reversal to account for it being upside down by Skia's
+     * coord convention.
+     */
+    GrCoordTransform(GrCoordSet sourceCoords, const SkMatrix& m, const GrTexture* texture = NULL) {
+        this->reset(sourceCoords, m, texture);
+    }
+
+    void reset(GrCoordSet sourceCoords, const GrTexture* texture) {
+        SkASSERT(NULL != texture);
+        this->reset(sourceCoords, GrEffect::MakeDivByTextureWHMatrix(texture), texture);
+    }
+
+    void reset(GrCoordSet sourceCoords, const SkMatrix& m, const GrTexture* texture = NULL) {
+        fSourceCoords = sourceCoords;
+        fMatrix = m;
+        fReverseY = NULL != texture && kBottomLeft_GrSurfaceOrigin == texture->origin();
+    }
+
+    bool operator== (const GrCoordTransform& other) const {
+        return fSourceCoords == other.fSourceCoords &&
+               fMatrix.cheapEqualTo(other.fMatrix) &&
+               fReverseY == other.fReverseY;
+    }
+
+    GrCoordSet sourceCoords() const { return fSourceCoords; }
+    const SkMatrix& getMatrix() const { return fMatrix; }
+    bool reverseY() const { return fReverseY; }
+
+private:
+    GrCoordSet fSourceCoords;
+    SkMatrix   fMatrix;
+    bool       fReverseY;
+
+    typedef SkNoncopyable INHERITED;
+};
+
+#endif