CoopAllTheThings/tools/mock_game/render_gl.cpp

// OpenGL backend for the mock game. Renders the animated pattern with scissored clears
// (glClear + glScissor -- all GL 1.1, exported straight from opengl32, so **no loader /
// submodule** is needed) and presents with SwapBuffers, so the OpenGL capture hook
// (SwapBuffers / wglSwapBuffers + glReadPixels) sees a genuine GL present.
//
// GL's framebuffer is bottom-left origin and the capture flips it vertically to top-down, so
// the frame-counter block is drawn at the GL *top* (y = h-block) to land at the captured
// image's top-left where the test samples it.
#include "render_backend.hpp"

#include <windows.h>

#include <GL/gl.h>

namespace coop::mock
{
namespace
{
class GlBackend : public RenderBackend
{
public:
	bool init(HWND hwnd, std::uint32_t width, std::uint32_t height) override
	{
		width_ = width;
		height_ = height;
		hwnd_ = hwnd;
		hdc_ = GetDC(hwnd);
		if (hdc_ == nullptr)
		{
			return false;
		}
		PIXELFORMATDESCRIPTOR pfd = {};
		pfd.nSize = sizeof(pfd);
		pfd.nVersion = 1;
		pfd.dwFlags = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER;
		pfd.iPixelType = PFD_TYPE_RGBA;
		pfd.cColorBits = 32;
		pfd.cAlphaBits = 8;
		pfd.iLayerType = PFD_MAIN_PLANE;
		const int pf = ChoosePixelFormat(hdc_, &pfd);
		if (pf == 0 || !SetPixelFormat(hdc_, pf, &pfd))
		{
			return false;
		}
		hglrc_ = wglCreateContext(hdc_); // legacy context is enough for GL 1.1 clears
		if (hglrc_ == nullptr || !wglMakeCurrent(hdc_, hglrc_))
		{
			return false;
		}
		// vsync if available (a game-like cadence; avoids spinning uncapped). Runtime extension
		// lookup -- no loader/submodule needed.
		using PFN_wglSwapIntervalEXT = BOOL(WINAPI*)(int);
		if (auto swap_interval = reinterpret_cast<PFN_wglSwapIntervalEXT>(wglGetProcAddress("wglSwapIntervalEXT")))
		{
			swap_interval(1);
		}
		return true;
	}

	void render_and_present(std::uint32_t frame) override
	{
		const GLsizei w = static_cast<GLsizei>(width_);
		const GLsizei h = static_cast<GLsizei>(height_);
		glViewport(0, 0, w, h);

		// Animated background (whole framebuffer).
		glDisable(GL_SCISSOR_TEST);
		glClearColor(static_cast<float>((frame * 2) % 256) / 255.0f, static_cast<float>((frame * 3) % 256) / 255.0f,
		             static_cast<float>((frame * 5) % 256) / 255.0f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);

		glEnable(GL_SCISSOR_TEST);
		// Moving vertical bar (full height).
		const std::uint32_t span = width_ > 24 ? width_ - 24 : 1;
		const GLint bx = static_cast<GLint>((frame * 4) % span);
		glScissor(bx, 0, 24, h);
		glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);

		// Frame-counter block at the GL top-left (y = h - block) so it lands top-left after the
		// capture's vertical flip.
		std::uint8_t r = 0, g = 0, b = 0;
		frame_to_rgb(frame, r, g, b);
		glScissor(0, h - static_cast<GLint>(kFrameBlock), static_cast<GLsizei>(kFrameBlock),
		          static_cast<GLsizei>(kFrameBlock));
		glClearColor(r / 255.0f, g / 255.0f, b / 255.0f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);
		glDisable(GL_SCISSOR_TEST);

		SwapBuffers(hdc_); // the capture hook intercepts this
	}

	[[nodiscard]] const char* name() const override
	{
		return "gl";
	}

	~GlBackend() override
	{
		wglMakeCurrent(nullptr, nullptr);
		if (hglrc_ != nullptr)
		{
			wglDeleteContext(hglrc_);
		}
		if (hdc_ != nullptr && hwnd_ != nullptr)
		{
			ReleaseDC(hwnd_, hdc_);
		}
	}

private:
	std::uint32_t width_ = 0;
	std::uint32_t height_ = 0;
	HWND hwnd_ = nullptr;
	HDC hdc_ = nullptr;
	HGLRC hglrc_ = nullptr;
};
} // namespace

std::unique_ptr<RenderBackend> create_gl_backend()
{
	return std::make_unique<GlBackend>();
}

} // namespace coop::mock