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#pragma once
#include <mbgl/renderer/backend_scope.hpp>
#include <mbgl/util/image.hpp>
#include <mbgl/util/size.hpp>
#include <mbgl/util/util.hpp>
#include <memory>
#include <mutex>
namespace mbgl {
namespace gl {
class Context;
using ProcAddress = void (*)();
using FramebufferID = uint32_t;
} // namespace gl
// The RendererBackend is used by the Renderer to facilitate
// the actual rendering.
class RendererBackend {
public:
RendererBackend();
virtual ~RendererBackend();
// 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 this backend is used for rendering. Implementations should ensure that a renderable
// object is bound and glClear/glDraw* calls can be done. They should also make sure that
// calling .bind() repeatedly is a no-op and that the appropriate gl::Context values are
// set to the current state.
virtual void bind() = 0;
virtual Size getFramebufferSize() const = 0;
protected:
// Called with the name of an OpenGL extension that should be loaded. RendererBackend 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 getExtensionFunctionPointer(const char*) = 0;
// Called when the backend's GL context needs to be made active or inactive. These are called,
// as a matched pair, exclusively through BackendScope, in two situations:
//
// 1. When releasing GL resources during Renderer destruction
// (Including calling CustomLayerHost::deinitialize during RenderCustomLayer destruction)
// 2. When renderering through Renderer::render()
// (Including calling CustomLayerHost::initialize for newly added custom layers and
// CustomLayerHost::deinitialize on layer removal)
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&);
void assumeScissorTest(bool);
// 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&);
void setScissorTest(bool);
protected:
std::unique_ptr<gl::Context> context;
private:
std::once_flag initialized;
friend class BackendScope;
};
MBGL_CONSTEXPR bool operator==(const RendererBackend& a, const RendererBackend& b) {
return &a == &b;
}
} // namespace mbgl
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