#define _POSIX_C_SOURCE 200809L

#include <assert.h>
#include <fcntl.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <unistd.h>
#include <xf86drm.h>
#include <xf86drmMode.h>

int main()
{
	int err;

	const int fd = open("/dev/dri/card1", O_RDWR | O_CLOEXEC);
	assert(fd != -1);

	drmModeRes *res = drmModeGetResources(fd);
	assert(res != nullptr);
	drmModeConnector *conn = drmModeGetConnector(fd, res->connectors[0]);
	assert(conn != nullptr);
	drmModeModeInfo mode = conn->modes[0];
	uint32_t conn_id = conn->connector_id;

	struct drm_mode_create_dumb create_req = {
		.width = mode.hdisplay,
		.height = mode.vdisplay,
		.bpp = 32,
	};
	err = ioctl(fd, DRM_IOCTL_MODE_CREATE_DUMB, &create_req);
	assert(err != -1);

	uint32_t fb_id;
	err = drmModeAddFB(
	    fd, create_req.width, create_req.height, 24, 32, create_req.pitch,
	    create_req.handle, &fb_id);
	assert(err == 0);

	err = drmModeSetCrtc(fd, res->crtcs[0], fb_id, 0, 0, &conn_id, 1, &mode);
	assert(err == 0);
	drmModeCrtc *crtc = drmModeGetCrtc(fd, res->crtcs[0]);
	assert(crtc != nullptr);

	struct drm_mode_map_dumb map_req = { .handle = create_req.handle };
	err = ioctl(fd, DRM_IOCTL_MODE_MAP_DUMB, &map_req);
	assert(err != -1);

	uint32_t *const fb = mmap(
	    0, create_req.size, PROT_READ | PROT_WRITE, MAP_SHARED, fd,
	    map_req.offset);
	assert(fb != MAP_FAILED);

	for (int y = 0; y < mode.vdisplay; ++y) {
		for (int x = 0; x < mode.hdisplay; ++x) {
			const uint8_t r = (x * 255) / mode.hdisplay;
			const uint8_t g = (y * 255) / mode.vdisplay;
			const uint8_t b = 128;
			fb[y * (create_req.pitch / 4) + x] = (r << 16) | (g << 8) | b;
		}
	}

	getchar();

	munmap(fb, create_req.size);
	struct drm_mode_destroy_dumb delete_req
	    = { .handle = create_req.handle };
	ioctl(fd, DRM_IOCTL_MODE_DESTROY_DUMB, &delete_req);

	drmModeSetCrtc(
	    fd, crtc->crtc_id, crtc->buffer_id, crtc->x, crtc->y, &conn_id, 1,
	    &crtc->mode);
	drmModeFreeCrtc(crtc);
	drmModeFreeConnector(conn);
	drmModeFreeResources(res);
	close(fd);

	return 0;
}