Implement texel buffers

src/gpu/GrBuffer.h

-/*
- * Copyright 2016 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#ifndef GrBuffer_DEFINED
-#define GrBuffer_DEFINED
-
-#include "GrGpuResource.h"
-
-class GrGpu;
-
-class GrBuffer : public GrGpuResource {
-public:
-    /**
-     * Computes a scratch key for a buffer with a "dynamic" access pattern. (Buffers with "static"
-     * and "stream" access patterns are disqualified by nature from being cached and reused.)
-     */
-    static void ComputeScratchKeyForDynamicBuffer(size_t size, GrBufferType intendedType,
-                                                  GrScratchKey* key) {
-        static const GrScratchKey::ResourceType kType = GrScratchKey::GenerateResourceType();
-        GrScratchKey::Builder builder(key, kType, 1 + (sizeof(size_t) + 3) / 4);
-        // TODO: There's not always reason to cache a buffer by type. In some (all?) APIs it's just
-        // a chunk of memory we can use/reuse for any type of data. We really only need to
-        // differentiate between the "read" types (e.g. kGpuToCpu_BufferType) and "draw" types.
-        builder[0] = intendedType;
-        builder[1] = (uint32_t)size;
-        if (sizeof(size_t) > 4) {
-            builder[2] = (uint32_t)((uint64_t)size >> 32);
-        }
-    }
-
-    GrAccessPattern accessPattern() const { return fAccessPattern; }
-
-    /**
-     * Returns true if the buffer is a wrapper around a CPU array. If true it
-     * indicates that map will always succeed and will be free.
-     */
-    bool isCPUBacked() const { return fCPUBacked; }
-
-    /**
-     * Maps the buffer to be written by the CPU.
-     *
-     * The previous content of the buffer is invalidated. It is an error
-     * to draw from the buffer while it is mapped. It may fail if the backend
-     * doesn't support mapping the buffer. If the buffer is CPU backed then
-     * it will always succeed and is a free operation. Once a buffer is mapped,
-     * subsequent calls to map() are ignored.
-     *
-     * Note that buffer mapping does not go through GrContext and therefore is
-     * not serialized with other operations.
-     *
-     * @return a pointer to the data or nullptr if the map fails.
-     */
-     void* map() {
-         if (!fMapPtr) {
-             this->onMap();
-         }
-         return fMapPtr;
-     }
-
-    /**
-     * Unmaps the buffer.
-     *
-     * The pointer returned by the previous map call will no longer be valid.
-     */
-     void unmap() {
-         SkASSERT(fMapPtr);
-         this->onUnmap();
-         fMapPtr = nullptr;
-     }
-
-    /**
-     * Returns the same ptr that map() returned at time of map or nullptr if the
-     * is not mapped.
-     *
-     * @return ptr to mapped buffer data or nullptr if buffer is not mapped.
-     */
-     void* mapPtr() const { return fMapPtr; }
-
-    /**
-     Queries whether the buffer has been mapped.
-
-     @return true if the buffer is mapped, false otherwise.
-     */
-     bool isMapped() const { return SkToBool(fMapPtr); }
-
-    /**
-     * Updates the buffer data.
-     *
-     * The size of the buffer will be preserved. The src data will be
-     * placed at the beginning of the buffer and any remaining contents will
-     * be undefined. srcSizeInBytes must be <= to the buffer size.
-     *
-     * The buffer must not be mapped.
-     *
-     * Note that buffer updates do not go through GrContext and therefore are
-     * not serialized with other operations.
-     *
-     * @return returns true if the update succeeds, false otherwise.
-     */
-    bool updateData(const void* src, size_t srcSizeInBytes) {
-        SkASSERT(!this->isMapped());
-        SkASSERT(srcSizeInBytes <= fGpuMemorySize);
-        return this->onUpdateData(src, srcSizeInBytes);
-    }
-
-protected:
-    GrBuffer(GrGpu* gpu, size_t gpuMemorySize, GrBufferType intendedType,
-             GrAccessPattern accessPattern, bool cpuBacked)
-        : INHERITED(gpu, kCached_LifeCycle),
-          fMapPtr(nullptr),
-          fGpuMemorySize(gpuMemorySize), // TODO: Zero for cpu backed buffers?
-          fAccessPattern(accessPattern),
-          fCPUBacked(cpuBacked) {
-        if (!fCPUBacked && SkIsPow2(fGpuMemorySize) && kDynamic_GrAccessPattern == fAccessPattern) {
-            GrScratchKey key;
-            ComputeScratchKeyForDynamicBuffer(fGpuMemorySize, intendedType, &key);
-            this->setScratchKey(key);
-        }
-    }
-
-    void* fMapPtr;
-
-private:
-    virtual size_t onGpuMemorySize() const { return fGpuMemorySize; }
-
-    virtual void onMap() = 0;
-    virtual void onUnmap() = 0;
-    virtual bool onUpdateData(const void* src, size_t srcSizeInBytes) = 0;
-
-    size_t            fGpuMemorySize;
-    GrAccessPattern   fAccessPattern;
-    bool              fCPUBacked;
-
-    typedef GrGpuResource INHERITED;
-};
-
-#endif