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#pragma once
#include <mbgl/map/map_observer.hpp>
#include <mbgl/util/image.hpp>
#include <mbgl/util/size.hpp>
#include <memory>
#include <mutex>
namespace mbgl {
namespace gl {
class Context;
using ProcAddress = void (*)();
using FramebufferID = uint32_t;
} // namespace gl
class BackendScope;
class Backend : public MapObserver {
public:
Backend();
virtual ~Backend();
// Returns the backend's context which manages OpenGL state.
gl::Context& getContext();
// Called prior to rendering to update the internally assumed OpenGL state.
virtual void updateAssumedState() = 0;
// Called when the map needs to be rendered; the backend should call Map::render() at some point
// in the near future. (Not called for Map::renderStill() mode.)
virtual void invalidate() = 0;
protected:
// Called with the name of an OpenGL extension that should be loaded. Backend implementations
// must call the API-specific version that obtains the function pointer for this function,
// or a null pointer if unsupported/unavailable.
virtual gl::ProcAddress initializeExtension(const char*) = 0;
// Called when the backend's GL context needs to be made active or inactive. These are called,
// as a matched pair, in four situations:
//
// 1. When releasing GL resources during Map destruction
// 2. When calling a CustomLayerInitializeFunction, during Map::addLayer
// 3. When calling a CustomLayerDeinitializeFunction, during Map::removeLayer
// 4. When rendering for Map::renderStill
//
// They are *not* called for Map::render; it is assumed that the correct context is already
// activated prior to calling Map::render.
virtual void activate() = 0;
virtual void deactivate() = 0;
// Reads the color pixel data from the currently bound framebuffer.
PremultipliedImage readFramebuffer(const Size&) const;
// A constant to signal that a framebuffer is bound, but with an unknown ID.
static constexpr const gl::FramebufferID ImplicitFramebufferBinding =
std::numeric_limits<gl::FramebufferID>::max();
// Tells the renderer that OpenGL state has already been set by the windowing toolkit.
// It sets the internal assumed state to the supplied values.
void assumeFramebufferBinding(gl::FramebufferID fbo);
void assumeViewport(int32_t x, int32_t y, const Size&);
// Returns true when assumed framebuffer binding hasn't changed from the implicit binding.
bool implicitFramebufferBound();
// Triggers an OpenGL state update if the internal assumed state doesn't match the
// supplied values.
void setFramebufferBinding(gl::FramebufferID fbo);
void setViewport(int32_t x, int32_t y, const Size&);
protected:
std::unique_ptr<gl::Context> context;
private:
std::once_flag initialized;
friend class BackendScope;
};
} // namespace mbgl
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