Create multiple window with SDL2 and sokol

multiwindow_SDL_sokol.cpp

#define SOKOL_IMPL
#define SOKOL_GLCORE

#include <SDL.h>

#include <sokol_gfx.h>
#include <sokol_log.h>

#include <iostream>
#include <sstream>
#include <array>

constexpr auto WndWidth = 640;
constexpr auto WndHeight = 480;
constexpr int g_WindowCount = 2;

struct WindowInfo {
	bool stop_rendering = false;
	bool shown = true;
	Uint32 winId;
	SDL_Window* win = nullptr;
	sg_color clearColor = { 0.5f, 0.5f, 0.5f, 1.0f };
	SDL_GLContext ctx;
	sg_attachments main_attach;
	sg_attachments win_attach;
};

void HandleWindowEvent(WindowInfo& wnd, SDL_Event e) {
	if (e.type == SDL_WINDOWEVENT) {
		if (e.window.event == SDL_WINDOWEVENT_MINIMIZED)
			wnd.stop_rendering = true;
		else if (e.window.event == SDL_WINDOWEVENT_RESTORED)
			wnd.stop_rendering = false;
		else if (e.window.event == SDL_WINDOWEVENT_CLOSE) {
			SDL_HideWindow(wnd.win);
			wnd.shown = false;
		}
	}
}

void CloseWindow(WindowInfo& win) {
	SDL_DestroyWindow(win.win); win.win = nullptr;
}

int main(int argc, char* argv[]) {

	if (SDL_Init(SDL_INIT_EVERYTHING) < 0) {
		std::cout << "error initializing SDL:" << SDL_GetError() << std::endl;
		return 1;
	}

	std::array<WindowInfo, g_WindowCount> windows;
	int preWndPosX = 0;
	int preWndPosY = 0;

	for (auto i = 0; i < g_WindowCount; ++i) {

		SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
		SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
		SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
		if (i > 0) {
			SDL_GL_MakeCurrent(windows.front().win, windows.front().ctx);
			SDL_GL_SetAttribute(SDL_GL_SHARE_WITH_CURRENT_CONTEXT, 1);
		}
		SDL_GL_LoadLibrary(nullptr);

		std::stringstream ss;
		ss << "Sokol with SDL " << i;

		WindowInfo win = {};

		win.win = SDL_CreateWindow(
			ss.str().c_str(),
			i == 0 ? SDL_WINDOWPOS_CENTERED : preWndPosX + WndWidth,
			i == 0 ? SDL_WINDOWPOS_CENTERED : preWndPosY,
			WndWidth,
			WndHeight,
			SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN
		);

		/* Create our opengl context and attach it to our window */
		win.ctx = SDL_GL_CreateContext(win.win);

		/* This makes our buffer swap syncronized with the monitor's vertical refresh */
		SDL_GL_SetSwapInterval(-1);

		win.winId = SDL_GetWindowID(win.win);

		if (i == 0) {
			// setup sokol_gfx
			sg_setup({
				.logger = {
					.func = slog_func
				},
				.environment = {
					.defaults = {
						.color_format = SG_PIXELFORMAT_RGBA8,
						.depth_format = SG_PIXELFORMAT_DEPTH_STENCIL,
						.sample_count = 1,
					} },
				});
			assert(sg_isvalid());
		}
		else {
			SDL_GL_MakeCurrent(windows.front().win, windows.front().ctx);
			win.clearColor = { 1.0f, 0.5f, 0.5f, 1.0f };
		}

		sg_image color_img = sg_make_image({
			.render_target = true,
			.width = WndWidth,
			.height = WndHeight,
			.pixel_format = SG_PIXELFORMAT_RGBA8,
			.sample_count = 1,
			.label = "color_img"
			});

		// create a framebuffer on the main gl context, this is where sokol-rendering goes into
		win.main_attach = sg_make_attachments({
			.colors = {
				{.image = color_img}
			},
			.depth_stencil = {
				.image = sg_make_image({
					.render_target = true,
					.width = WndWidth,
					.height = WndHeight,
					.pixel_format = SG_PIXELFORMAT_DEPTH_STENCIL,
					.label = "depth_img"
				}),
			},
			.label = "main_attachment"
			});
		assert(glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE);

		// create a framebuffer on the window gl context which shares its renderbuffers with
		// the main-context framebuffer, this framebuffer will be the source for a blit-framebuffer operation
		SDL_GL_MakeCurrent(win.win, win.ctx);
		win.win_attach = sg_make_attachments({
			.colors = {
				{.image = color_img}
			},
			.label = "win_attach"
			});
		assert(glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE);

		windows[i] = win;
		SDL_GetWindowPosition(win.win, &preWndPosX, &preWndPosY);
	}

	SDL_GL_MakeCurrent(windows.front().win, windows.front().ctx);

	// create a vertex buffer
	float vertices[] = {
		// positions            colors
		-0.5f,  0.5f, 0.5f,     1.0f, 0.0f, 0.0f, 1.0f,
		 0.5f,  0.5f, 0.5f,     0.0f, 1.0f, 0.0f, 1.0f,
		 0.5f, -0.5f, 0.5f,     0.0f, 0.0f, 1.0f, 1.0f,
		-0.5f, -0.5f, 0.5f,     1.0f, 1.0f, 0.0f, 1.0f,
	};
	sg_buffer_desc vbuf_desc = {
		.data = SG_RANGE(vertices)
	};
	sg_buffer vbuf = sg_make_buffer(&vbuf_desc);

	// create an index buffer
	uint16_t indices[] = {
		0, 1, 2,    // first triangle
		0, 2, 3,    // second triangle
	};
	sg_buffer_desc ibuf_desc = {
		.type = SG_BUFFERTYPE_INDEXBUFFER,
		.data = SG_RANGE(indices)
	};
	sg_buffer ibuf = sg_make_buffer(&ibuf_desc);

	// define the resource bindings
	sg_bindings bind = {
		.vertex_buffers = { vbuf },
		.index_buffer = ibuf
	};

	// create a shader (use vertex attribute locations)
	sg_shader shd = sg_make_shader({
			.vs = {
				.source =
					"#version 330\n"
					"layout(location=0) in vec4 position;\n"
					"layout(location=1) in vec4 color0;\n"
					"out vec4 color;\n"
					"void main() {\n"
					"  gl_Position = position;\n"
					"  color = color0;\n"
					"}\n"
			},
			.fs = {
				.source =
					"#version 330\n"
					"in vec4 color;\n"
					"out vec4 frag_color;\n"
					"void main() {\n"
					"  frag_color = color;\n"
					"}\n"
			},
		});

	// create a pipeline object (default render state is fine)
	sg_pipeline pip = sg_make_pipeline({
		.shader = shd,
		.layout = {
			.attrs = {
				// vertex attrs can also be bound by location instead of name
				{.offset = 0, .format = SG_VERTEXFORMAT_FLOAT3 },
				{.offset = 12, .format = SG_VERTEXFORMAT_FLOAT4 }
			}
		},
		.index_type = SG_INDEXTYPE_UINT16,
	});

	// draw loop
	SDL_Event e;
	bool bQuit = false;
	while (!bQuit) {
		while (SDL_PollEvent(&e) != 0) {
			if (e.type == SDL_QUIT)
				bQuit = true;

			for (auto& w : windows) {
				if (e.window.windowID == w.winId)
					HandleWindowEvent(w, e);
			}
		}

		const auto& main_win = windows.front();
		bQuit = !main_win.shown;
		SDL_GL_MakeCurrent(main_win.win, main_win.ctx);
		sg_reset_state_cache();

		for (const auto& w : windows) {
			if (w.stop_rendering)
				continue;
			sg_begin_pass({
				.action = {
					.colors = {
						{
							.load_action = SG_LOADACTION_CLEAR,
							.clear_value = w.clearColor
						}
					}
				},
				.attachments = w.main_attach,
			});
			sg_apply_pipeline(pip);
			sg_apply_bindings(bind);
			sg_draw(0, 6, 1);
			sg_end_pass();
		}
		sg_commit();

		for (const auto& w : windows) {
			if (w.stop_rendering)
				continue;
			SDL_GL_MakeCurrent(w.win, w.ctx);
			glDisable(GL_FRAMEBUFFER_SRGB);
			glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
			const auto win_gl_info = sg_gl_query_attachments_info(w.win_attach);
			glBindFramebuffer(GL_READ_FRAMEBUFFER, win_gl_info.framebuffer);
			glBlitFramebuffer(0, 0, WndWidth, WndHeight, 0, 0, WndWidth, WndHeight, GL_COLOR_BUFFER_BIT, GL_LINEAR);
			SDL_GL_SwapWindow(w.win);
		}
	}

	/* cleanup */
	sg_shutdown();
	for (auto& w : windows)
		CloseWindow(w);
	SDL_Quit();

	return 0;
}