mitch030504--AstroQuest-Frame/quest-host/cpp/gl_frames.h

// SPDX-License-Identifier: GPL-2.0-or-later
#pragma once

// The GL side of showing the emulator's frames, shared by the OpenXR host and by the self test
// that exercises the same path without a headset session.

#include <cstdint>
#include <vector>

// Extension entry points (EGL images over hardware buffers) are only declared on request.
#define EGL_EGLEXT_PROTOTYPES
#define GL_GLEXT_PROTOTYPES
#include <EGL/egl.h>
#include <EGL/eglext.h>
#include <GLES3/gl3.h>
// The extension header relies on the types the one above defines.
#include <GLES2/gl2ext.h>

struct AHardwareBuffer;
class CoreProcess;

/// An OpenGL ES 3 context that draws to nothing: everything is rendered to textures.
struct GlContext {
    EGLDisplay display{EGL_NO_DISPLAY};
    EGLConfig config{};
    EGLContext context{EGL_NO_CONTEXT};
    EGLSurface surface{EGL_NO_SURFACE};

    bool Create();
    void Destroy();
};

/// The images the emulator renders into: hardware buffers handed to it as dma-bufs, each of them
/// also a GL texture here, so that a frame gets from one process to the other without a copy.
class FrameBuffers {
public:
    static constexpr uint32_t Count = 3;

    /// Allocates the buffers and offers them to the core. Needs a current GL context.
    bool Create(EGLDisplay display, uint32_t width, uint32_t height, CoreProcess& core);
    void Destroy(EGLDisplay display);

    bool IsValid(uint32_t index) const {
        return index < textures.size();
    }
    GLuint Texture(uint32_t index) const {
        return textures[index];
    }

private:
    std::vector<AHardwareBuffer*> buffers;
    std::vector<EGLImageKHR> images;
    std::vector<GLuint> textures;
};

/// Copies a frame to the framebuffer that is bound, upside up and in the right color encoding.
class FrameBlitter {
public:
    bool Create();
    void Destroy();

    /// `srgb_target` is for sRGB targets: they encode whatever is written to them, while the
    /// emulator delivers values that are display-ready already. Where the GPU can be told to
    /// leave that encoding out, the frame is written as it is; elsewhere it is decoded first,
    /// which costs a power function per pixel.
    void Draw(GLuint texture, uint32_t width, uint32_t height, bool swap_red_blue,
              bool srgb_target) const;

    /// Whether frames go into sRGB targets unchanged (see Draw).
    bool WritesUnencoded() const {
        return write_control;
    }

private:
    GLuint program{};
    GLuint vertex_array{};
    GLint uniform_swap{-1};
    GLint uniform_decode{-1};
    bool write_control{};
};