skia2/include/gpu/GrGeometryProcessor.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 GrGeometryProcessor_DEFINED
#define GrGeometryProcessor_DEFINED

#include "GrProcessor.h"
class GrBackendGeometryProcessorFactory;

/**
 * A GrGeomteryProcessor is used to perform computation in the vertex shader and
 * add support for custom vertex attributes. A GrGemeotryProcessor is typically
 * tied to the code that does a specific type of high-level primitive rendering
 * (e.g. anti-aliased circle rendering). The GrGeometryProcessor used for a draw is
 * specified using GrDrawState. There can only be one geometry processor active for
 * a draw. The custom vertex attributes required by the geometry processor must be
 * added to the vertex attribute array specified on the GrDrawState.
 * GrGeometryProcessor subclasses should be immutable after construction.
 */
class GrGeometryProcessor : public GrProcessor {
public:
    GrGeometryProcessor() {}

    virtual const GrBackendGeometryProcessorFactory& getFactory() const = 0;

    /*
     * This only has a max because GLProgramsTest needs to generate test arrays, and these have to
     * be static
     * TODO make this truly dynamic
     */
    static const int kMaxVertexAttribs = 2;
    typedef SkTArray<GrShaderVar, true> VertexAttribArray;

    const VertexAttribArray& getVertexAttribs() const { return fVertexAttribs; }

    bool isEqual(const GrGeometryProcessor& that) const {
        if (&this->getFactory() != &that.getFactory()) {
            return false;
        }
        bool result = this->onIsEqual(that);
#ifdef SK_DEBUG
        if (result) {
            this->assertTexturesEqual(that);
        }
#endif
        return result;
    }

protected:
    /**
     * Subclasses call this from their constructor to register vertex attributes (at most
     * kMaxVertexAttribs). This must only be called from the constructor because GrProcessors are
     * immutable.
     */
    const GrShaderVar& addVertexAttrib(const GrShaderVar& var) {
        SkASSERT(fVertexAttribs.count() < kMaxVertexAttribs);
        return fVertexAttribs.push_back(var);
    }

private:
    virtual bool onIsEqual(const GrGeometryProcessor&) const = 0;

    SkSTArray<kMaxVertexAttribs, GrShaderVar, true> fVertexAttribs;

    typedef GrProcessor INHERITED;
};

/**
 * This creates an effect outside of the effect memory pool. The effect's destructor will be called
 * at global destruction time. NAME will be the name of the created GrProcessor.
 */
#define GR_CREATE_STATIC_GEOMETRY_PROCESSOR(NAME, GP_CLASS, ARGS)                                 \
static SkAlignedSStorage<sizeof(GP_CLASS)> g_##NAME##_Storage;                                    \
static GrGeometryProcessor* NAME SkNEW_PLACEMENT_ARGS(g_##NAME##_Storage.get(), GP_CLASS, ARGS);  \
static SkAutoTDestroy<GrGeometryProcessor> NAME##_ad(NAME);

#endif