Make texture domain a helper so that it can be incorporated into other effects.

src/gpu/effects/GrTextureDomain.h

+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrTextureDomainEffect_DEFINED
+#define GrTextureDomainEffect_DEFINED
+
+#include "GrSingleTextureEffect.h"
+#include "gl/GrGLEffect.h"
+
+class GrGLShaderBuilder;
+struct SkRect;
+
+/**
+ * Limits a texture's lookup coordinates to a domain. Samples outside the domain are either clamped
+ * the edge of the domain or result in a vec4 of zeros (decal mode). The domain is clipped to
+ * normalized texture coords ([0,1]x[0,1] square). Bilinear filtering can cause texels outside the
+ * domain to affect the read value unless the caller considers this when calculating the domain.
+ */
+class GrTextureDomain {
+public:
+    enum Mode {
+        kIgnore_Mode,  // Ignore the texture domain rectangle.
+        kClamp_Mode,   // Clamp texture coords to the domain rectangle.
+        kDecal_Mode,   // Treat the area outside the domain rectangle as fully transparent.
+
+        kLastMode = kDecal_Mode
+    };
+    static const int kModeCount = kLastMode + 1;
+
+    /**
+     * @param index     Pass a value >= 0 if using multiple texture domains in the same effect.
+     *                  It is used to keep inserted variables from causing name collisions.
+     */
+    GrTextureDomain(const SkRect& domain, Mode, int index = -1);
+
+    const SkRect& domain() const { return fDomain; }
+    Mode mode() const { return fMode; }
+
+    /* Computes a domain that bounds all the texels in texelRect. Note that with bilerp enabled
+       texels neighboring the domain may be read. */
+    static const SkRect MakeTexelDomain(const GrTexture* texture, const SkIRect& texelRect) {
+        SkScalar wInv = SK_Scalar1 / texture->width();
+        SkScalar hInv = SK_Scalar1 / texture->height();
+        SkRect result = {
+            texelRect.fLeft * wInv,
+            texelRect.fTop * hInv,
+            texelRect.fRight * wInv,
+            texelRect.fBottom * hInv
+        };
+        return result;
+    }
+
+    bool operator== (const GrTextureDomain& that) const {
+        return fMode == that.fMode && fDomain == that.fDomain;
+    }
+
+    /**
+     * A GrGLEffect subclass that corresponds to a GrEffect subclass that uses GrTextureDomain
+     * should include this helper. It generates the texture domain GLSL, produces the part of the
+     * effect key that reflects the texture domain code, and performs the uniform uploads necessary
+     * for texture domains.
+     */
+    class GLDomain {
+    public:
+        GLDomain() {
+            fPrevDomain[0] = SK_FloatNaN;
+            SkDEBUGCODE(fMode = (Mode) -1;)
+        }
+
+        /**
+         * Call this from GrGLEffect::emitCode() to sample the texture W.R.T. the domain and mode.
+         *
+         * @param outcolor  name of vec4 variable to hold the sampled color.
+         * @param inCoords  name of vec2 variable containing the coords to be used with the domain.
+         *                  It is assumed that this is a variable and not an expression.
+         * @param inModulateColor   if non-NULL the sampled color will be modulated with this
+         *                          expression before being written to outColor.
+         */
+        void sampleTexture(GrGLShaderBuilder* builder,
+                           const GrTextureDomain& textureDomain,
+                           const char* outColor,
+                           const SkString& inCoords,
+                           const GrGLEffect::TextureSampler sampler,
+                           const char* inModulateColor = NULL);
+
+        /**
+         * Call this from GrGLEffect::setData() to upload uniforms necessary for the texture domain.
+         * The rectangle is automatically adjusted to account for the texture's origin.
+         */
+        void setData(const GrGLUniformManager& uman, const GrTextureDomain& textureDomain,
+                     GrSurfaceOrigin textureOrigin);
+
+        enum {
+            kDomainKeyBits = 2, // See DomainKey().
+        };
+
+        /**
+         * GrGLEffect::GenKey() must call this and include the returned value in it's computed key.
+         * The returned will be limited to the lower kDomainKeyBits bits.
+         */
+        static GrGLEffect::EffectKey DomainKey(const GrTextureDomain& domain) {
+            GR_STATIC_ASSERT(kModeCount <= 4);
+            return domain.mode();
+        }
+
+    private:
+        SkDEBUGCODE(Mode                  fMode;)
+        GrGLUniformManager::UniformHandle fDomainUni;
+        SkString                          fDomainName;
+        GrGLfloat                         fPrevDomain[4];
+    };
+
+protected:
+    Mode    fMode;
+    SkRect  fDomain;
+    int     fIndex;
+
+    typedef GrSingleTextureEffect INHERITED;
+};
+
+class GrGLTextureDomainEffect;
+
+/**
+ * A basic texture effect that uses GrTextureDomain.
+ */
+class GrTextureDomainEffect : public GrSingleTextureEffect {
+
+public:
+    static GrEffectRef* Create(GrTexture*,
+                               const SkMatrix&,
+                               const SkRect& domain,
+                               GrTextureDomain::Mode,
+                               GrTextureParams::FilterMode filterMode,
+                               GrCoordSet = kLocal_GrCoordSet);
+
+    virtual ~GrTextureDomainEffect();
+
+    static const char* Name() { return "TextureDomain"; }
+
+    typedef GrGLTextureDomainEffect GLEffect;
+
+    virtual const GrBackendEffectFactory& getFactory() const SK_OVERRIDE;
+    virtual void getConstantColorComponents(GrColor* color, uint32_t* validFlags) const SK_OVERRIDE;
+
+    const GrTextureDomain& textureDomain() const { return fTextureDomain; }
+
+protected:
+    GrTextureDomain fTextureDomain;
+
+private:
+    GrTextureDomainEffect(GrTexture*,
+                          const SkMatrix&,
+                          const SkRect& domain,
+                          GrTextureDomain::Mode,
+                          GrTextureParams::FilterMode,
+                          GrCoordSet);
+
+    virtual bool onIsEqual(const GrEffect&) const SK_OVERRIDE;
+
+    GR_DECLARE_EFFECT_TEST;
+
+    typedef GrSingleTextureEffect INHERITED;
+};
+
+#endif