Inital commit of libotd.

backend/drm/drm.c

@@ -0,0 +1,466 @@
+#include "otd.h"
+#include "drm.h"
+#include "event.h"
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <inttypes.h>
+#include <errno.h>
+#include <xf86drm.h>
+#include <xf86drmMode.h>
+#include <drm_mode.h>
+#include <EGL/egl.h>
+#include <EGL/eglext.h>
+#include <gbm.h>
+#include <GLES3/gl3.h>
+
+static const char *conn_name[] = {
+	[DRM_MODE_CONNECTOR_Unknown]     = "Unknown",
+	[DRM_MODE_CONNECTOR_VGA]         = "VGA",
+	[DRM_MODE_CONNECTOR_DVII]        = "DVI-I",
+	[DRM_MODE_CONNECTOR_DVID]        = "DVI-D",
+	[DRM_MODE_CONNECTOR_DVIA]        = "DVI-A",
+	[DRM_MODE_CONNECTOR_Composite]   = "Composite",
+	[DRM_MODE_CONNECTOR_SVIDEO]      = "SVIDEO",
+	[DRM_MODE_CONNECTOR_LVDS]        = "LVDS",
+	[DRM_MODE_CONNECTOR_Component]   = "Component",
+	[DRM_MODE_CONNECTOR_9PinDIN]     = "DIN",
+	[DRM_MODE_CONNECTOR_DisplayPort] = "DP",
+	[DRM_MODE_CONNECTOR_HDMIA]       = "HDMI-A",
+	[DRM_MODE_CONNECTOR_HDMIB]       = "HDMI-B",
+	[DRM_MODE_CONNECTOR_TV]          = "TV",
+	[DRM_MODE_CONNECTOR_eDP]         = "eDP",
+	[DRM_MODE_CONNECTOR_VIRTUAL]     = "Virtual",
+	[DRM_MODE_CONNECTOR_DSI]         = "DSI",
+};
+
+// EGL extensions
+PFNEGLGETPLATFORMDISPLAYEXTPROC get_platform_display;
+PFNEGLCREATEPLATFORMWINDOWSURFACEEXTPROC create_platform_window_surface;
+
+static bool egl_exts()
+{
+	get_platform_display = (PFNEGLGETPLATFORMDISPLAYEXTPROC)
+		eglGetProcAddress("eglGetPlatformDisplayEXT");
+
+	create_platform_window_surface = (PFNEGLCREATEPLATFORMWINDOWSURFACEEXTPROC)
+		eglGetProcAddress("eglCreatePlatformWindowSurfaceEXT");
+
+	return get_platform_display && create_platform_window_surface;
+}
+
+bool egl_get_config(EGLDisplay disp, EGLConfig *out)
+{
+	EGLint count = 0, matched = 0, ret;
+
+	ret = eglGetConfigs(disp, NULL, 0, &count);
+	if (ret == EGL_FALSE || count == 0) {
+		return false;
+	}
+
+	EGLConfig configs[count];
+
+	ret = eglChooseConfig(disp, NULL, configs, count, &matched);
+	if (ret == EGL_FALSE) {
+		return false;
+	}
+
+	for (int i = 0; i < matched; ++i) {
+		EGLint gbm_format;
+
+		if (!eglGetConfigAttrib(disp,
+					configs[i],
+					EGL_NATIVE_VISUAL_ID,
+					&gbm_format))
+			continue;
+
+		if (gbm_format == GBM_FORMAT_XRGB8888) {
+			*out = configs[i];
+			return true;
+		}
+	}
+
+	return false;
+}
+
+bool init_renderer(struct otd *otd)
+{
+	if (!egl_exts()) {
+		fprintf(stderr, "Could not get EGL extensions\n");
+		return false;
+	}
+
+	otd->gbm = gbm_create_device(otd->fd);
+	if (!otd->gbm) {
+		fprintf(stderr, "Could not create gbm device: %s\n", strerror(errno));
+		return false;
+	}
+
+	if (eglBindAPI(EGL_OPENGL_ES_API) == EGL_FALSE) {
+		fprintf(stderr, "Could not bind GLES3 API\n");
+		goto error_gbm;
+	}
+
+	otd->egl.disp = get_platform_display(EGL_PLATFORM_GBM_MESA, otd->gbm, NULL);
+	if (otd->egl.disp == EGL_NO_DISPLAY) {
+		fprintf(stderr, "Could not create EGL display\n");
+		goto error_gbm;
+	}
+
+	if (eglInitialize(otd->egl.disp, NULL, NULL) == EGL_FALSE) {
+		fprintf(stderr, "Could not initalise EGL\n");
+		goto error_egl;
+	}
+
+	if (!egl_get_config(otd->egl.disp, &otd->egl.conf)) {
+		fprintf(stderr, "Could not get EGL config\n");
+		goto error_egl;
+	}
+
+	static const EGLint attribs[] = {EGL_CONTEXT_CLIENT_VERSION, 3, EGL_NONE};
+	otd->egl.context = eglCreateContext(otd->egl.disp, otd->egl.conf, EGL_NO_CONTEXT, attribs);
+	if (otd->egl.context == EGL_NO_CONTEXT) {
+		fprintf(stderr, "Could not create EGL context\n");
+		goto error_egl;
+	}
+
+	return true;
+
+error_egl:
+	eglTerminate(otd->egl.disp);
+	eglReleaseThread();
+	eglMakeCurrent(EGL_NO_DISPLAY, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);
+
+error_gbm:
+	gbm_device_destroy(otd->gbm);
+
+	return false;
+}
+
+void destroy_renderer(struct otd *otd)
+{
+	if (!otd)
+		return;
+
+	eglDestroyContext(otd->egl.disp, otd->egl.context);
+	eglTerminate(otd->egl.disp);
+	eglReleaseThread();
+	eglMakeCurrent(EGL_NO_DISPLAY, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);
+
+	gbm_device_destroy(otd->gbm);
+}
+
+void scan_connectors(struct otd *otd)
+{
+	drmModeRes *res = drmModeGetResources(otd->fd);
+	if (!res)
+		return;
+
+	// I don't know if this needs to be allocated with realloc like this,
+	// as it may not even be possible for the number of connectors to change.
+	// I'll just have to see how DisplayPort MST works with DRM.
+	if ((size_t)res->count_connectors > otd->display_len) {
+		struct otd_display *new = realloc(otd->displays, sizeof *new * res->count_connectors);
+		if (!new)
+			goto error;
+
+		for (int i = otd->display_len; i < res->count_connectors; ++i) {
+			new[i] = (struct otd_display) {
+				.state = OTD_DISP_INVALID,
+				.otd = otd,
+			};
+		}
+
+		otd->display_len = res->count_connectors;
+		otd->displays = new;
+	}
+
+	for (int i = 0; i < res->count_connectors; ++i) {
+		struct otd_display *disp = &otd->displays[i];
+		drmModeConnector *conn = drmModeGetConnector(otd->fd, res->connectors[i]);
+		if (!conn)
+			continue;
+
+		if (otd->displays[i].state == OTD_DISP_INVALID) {
+			disp->state = OTD_DISP_DISCONNECTED;
+			disp->connector = res->connectors[i];
+			snprintf(disp->name, sizeof disp->name, "%s-%"PRIu32,
+				 conn_name[conn->connector_type],
+				 conn->connector_type_id);
+		}
+
+		if (disp->state == OTD_DISP_DISCONNECTED &&
+		    conn->connection == DRM_MODE_CONNECTED) {
+			disp->state = OTD_DISP_NEEDS_MODESET;
+			event_add(otd, disp, OTD_EV_DISPLAY_ADD);
+
+		} else if (disp->state == OTD_DISP_CONNECTED &&
+		    conn->connection != DRM_MODE_CONNECTED) {
+			disp->state = OTD_DISP_DISCONNECTED;
+			event_add(otd, disp, OTD_EV_DISPLAY_REM);
+		}
+
+		drmModeFreeConnector(conn);
+	}
+
+error:
+	drmModeFreeResources(res);
+}
+
+static void free_fb(struct gbm_bo *bo, void *data)
+{
+	uint32_t *id = data;
+
+	if (id && *id)
+		drmModeRmFB(gbm_bo_get_fd(bo), *id);
+
+	free(id);
+}
+
+static uint32_t get_fb_for_bo(int fd, struct gbm_bo *bo)
+{
+	uint32_t *id = gbm_bo_get_user_data(bo);
+
+	if (id)
+		return *id;
+
+	id = calloc(1, sizeof *id);
+	if (!id)
+		return 0;
+
+	drmModeAddFB(fd, gbm_bo_get_width(bo), gbm_bo_get_height(bo), 24, 32,
+		     gbm_bo_get_stride(bo), gbm_bo_get_handle(bo).u32, id);
+
+	gbm_bo_set_user_data(bo, id, free_fb);
+
+	return *id;
+}
+
+static void init_display_renderer(struct otd *otd, struct otd_display *disp)
+{
+	disp->gbm = gbm_surface_create(otd->gbm,
+				       disp->width, disp->height,
+				       GBM_FORMAT_XRGB8888,
+				       GBM_BO_USE_SCANOUT | GBM_BO_USE_RENDERING);
+	if (!disp->gbm)
+		return;
+
+	disp->egl = create_platform_window_surface(otd->egl.disp, otd->egl.conf,
+						   disp->gbm, NULL);
+	if (disp->egl == EGL_NO_SURFACE)
+		return;
+
+	// Render black frame
+
+	eglMakeCurrent(otd->egl.disp, disp->egl, disp->egl, otd->egl.context);
+
+	glViewport(0, 0, disp->width, disp->height);
+	glClearColor(0.0, 0.0, 0.0, 1.0);
+	glClear(GL_COLOR_BUFFER_BIT);
+
+	eglSwapBuffers(otd->egl.disp, disp->egl);
+
+	struct gbm_bo *bo = gbm_surface_lock_front_buffer(disp->gbm);
+	uint32_t fb_id = get_fb_for_bo(otd->fd, bo);
+
+	drmModeSetCrtc(otd->fd, disp->crtc, fb_id, 0, 0,
+		       &disp->connector, 1, disp->active_mode);
+	drmModePageFlip(otd->fd, disp->crtc, fb_id, DRM_MODE_PAGE_FLIP_EVENT, disp);
+
+	gbm_surface_release_buffer(disp->gbm, bo);
+}
+
+static drmModeModeInfo *select_mode(size_t num_modes,
+				    drmModeModeInfo modes[static num_modes],
+				    drmModeCrtc *old_crtc,
+				    const char *str)
+{
+	if (strcmp(str, "preferred") == 0)
+		return &modes[0];
+
+	if (strcmp(str, "current") == 0) {
+		if (!old_crtc) {
+			fprintf(stderr, "Display does not have currently configured mode\n");
+			return NULL;
+		}
+
+		for (size_t i = 0; i < num_modes; ++i) {
+			if (memcmp(&modes[i], &old_crtc->mode, sizeof modes[0]) == 0)
+				return &modes[i];
+		}
+
+		// We should never get here
+		assert(0);
+	}
+
+	unsigned width = 0;
+	unsigned height = 0;
+	unsigned rate = 0;
+	int ret;
+
+	if ((ret = sscanf(str, "%ux%u@%u", &width, &height, &rate)) != 2 && ret != 3) {
+		fprintf(stderr, "Invalid modesetting string\n");
+		return NULL;
+	}
+
+	for (size_t i = 0; i < num_modes; ++i) {
+		if (modes[i].hdisplay == width &&
+		    modes[i].vdisplay == height &&
+		    (!rate || modes[i].vrefresh == rate))
+			return &modes[i];
+	}
+
+	return NULL;
+}
+
+bool modeset_str(struct otd *otd, struct otd_display *disp, const char *str)
+{
+	drmModeConnector *conn = drmModeGetConnector(otd->fd, disp->connector);
+	if (!conn || conn->connection != DRM_MODE_CONNECTED || conn->count_modes == 0)
+		goto error;
+
+	disp->num_modes = conn->count_modes;
+	disp->modes = malloc(sizeof *disp->modes * disp->num_modes);
+	if (!disp->modes)
+		goto error;
+	memcpy(disp->modes, conn->modes, sizeof *disp->modes * disp->num_modes);
+
+	drmModeEncoder *curr_enc = drmModeGetEncoder(otd->fd, conn->encoder_id);
+	if (curr_enc) {
+		disp->old_crtc = drmModeGetCrtc(otd->fd, curr_enc->crtc_id);
+		free(curr_enc);
+	}
+
+	disp->active_mode = select_mode(disp->num_modes, disp->modes, disp->old_crtc, str);
+	if (!disp->active_mode) {
+		fprintf(stderr, "Could not find mode '%s' for %s\n", str, disp->name);
+		goto error;
+	}
+
+	fprintf(stderr, "Configuring %s with mode %ux%u@%u\n",
+		disp->name, disp->active_mode->hdisplay, disp->active_mode->vdisplay,
+		disp->active_mode->vrefresh);
+
+	drmModeRes *res = drmModeGetResources(otd->fd);
+	if (!res)
+		goto error;
+
+	bool success = false;
+	for (int i = 0; !success && i < conn->count_encoders; ++i) {
+		drmModeEncoder *enc = drmModeGetEncoder(otd->fd, conn->encoders[i]);
+		if (!enc)
+			continue;
+
+		for (int j = 0; j < res->count_crtcs; ++j) {
+			if ((enc->possible_crtcs & (1 << j)) == 0)
+				continue;
+
+			if ((otd->taken_crtcs & (1 << j)) == 0) {
+				otd->taken_crtcs |= 1 << j;
+				disp->crtc = res->crtcs[j];
+
+				success = true;
+				break;
+			}
+		}
+
+		drmModeFreeEncoder(enc);
+	}
+
+	drmModeFreeResources(res);
+
+	if (!success)
+		goto error;
+
+	disp->state = OTD_DISP_CONNECTED;
+	drmModeFreeConnector(conn);
+
+	disp->width = disp->active_mode->hdisplay;
+	disp->height = disp->active_mode->vdisplay;
+
+	init_display_renderer(otd, disp);
+
+	return true;
+error:
+	disp->state = OTD_DISP_DISCONNECTED;
+	drmModeFreeConnector(conn);
+
+	event_add(otd, disp, OTD_EV_DISPLAY_REM);
+
+	return false;
+}
+
+
+void page_flip_handler(int fd,
+		       unsigned seq,
+		       unsigned tv_sec,
+		       unsigned tv_usec,
+		       void *user)
+{
+	struct otd_display *disp = user;
+
+	disp->pageflip_pending = true;
+	if (!disp->cleanup)
+		event_add(disp->otd, disp, OTD_EV_RENDER);
+}
+
+void destroy_display_renderer(struct otd *otd, struct otd_display *disp)
+{
+	if (!otd || !disp || disp->state != OTD_DISP_CONNECTED)
+		return;
+
+	drmModeCrtc *crtc = disp->old_crtc;
+	if (crtc) {
+		drmEventContext event = {
+			.version = DRM_EVENT_CONTEXT_VERSION,
+			.page_flip_handler = page_flip_handler,
+		};
+
+		disp->cleanup = true;
+		while (disp->pageflip_pending)
+			drmHandleEvent(otd->fd, &event);
+
+		drmModeSetCrtc(otd->fd, crtc->crtc_id, crtc->buffer_id,
+			       crtc->x, crtc->y, &disp->connector,
+			       1, &crtc->mode);
+		drmModeFreeCrtc(crtc);
+	}
+
+	eglDestroySurface(otd->egl.disp, disp->egl);
+	gbm_surface_destroy(disp->gbm);
+
+	free(disp->modes);
+}
+
+void get_drm_event(struct otd *otd)
+{
+	drmEventContext event = {
+		.version = DRM_EVENT_CONTEXT_VERSION,
+		.page_flip_handler = page_flip_handler,
+	};
+
+	drmHandleEvent(otd->fd, &event);
+}
+
+void rendering_begin(struct otd_display *disp)
+{
+	struct otd *otd = disp->otd;
+	eglMakeCurrent(otd->egl.disp, disp->egl, disp->egl, otd->egl.context);
+}
+
+void rendering_end(struct otd_display *disp)
+{
+	struct otd *otd = disp->otd;
+	eglSwapBuffers(otd->egl.disp, disp->egl);
+
+	struct gbm_bo *bo = gbm_surface_lock_front_buffer(disp->gbm);
+	uint32_t fb_id = get_fb_for_bo(otd->fd, bo);
+
+	drmModePageFlip(otd->fd, disp->crtc, fb_id, DRM_MODE_PAGE_FLIP_EVENT, disp);
+
+	gbm_surface_release_buffer(disp->gbm, bo);
+
+	disp->pageflip_pending = false;
+}

backend/drm/drm.h

@@ -0,0 +1,54 @@
+#ifndef DRM_H
+#define DRM_H
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <xf86drmMode.h>
+#include <EGL/egl.h>
+#include <gbm.h>
+
+enum otd_display_state {
+	OTD_DISP_INVALID,
+	OTD_DISP_DISCONNECTED,
+	OTD_DISP_NEEDS_MODESET,
+	OTD_DISP_CONNECTED,
+};
+
+struct otd_display {
+	struct otd *otd;
+
+	enum otd_display_state state;
+	uint32_t connector;
+	char name[16];
+
+	size_t num_modes;
+	drmModeModeInfo *modes;
+	drmModeModeInfo *active_mode;
+
+	uint32_t width;
+	uint32_t height;
+
+	uint32_t crtc;
+	drmModeCrtc *old_crtc;
+
+	struct gbm_surface *gbm;
+	EGLSurface *egl;
+	uint32_t fb_id;
+
+	bool pageflip_pending;
+	bool cleanup;
+};
+
+bool init_renderer(struct otd *otd);
+void destroy_renderer(struct otd *otd);
+
+void scan_connectors(struct otd *otd);
+bool modeset_str(struct otd *otd, struct otd_display *disp, const char *str);
+void destroy_display_renderer(struct otd *otd, struct otd_display *disp);
+
+void get_drm_event(struct otd *otd);
+
+void rendering_begin(struct otd_display *disp);
+void rendering_end(struct otd_display *disp);
+
+#endif

backend/drm/event.c

@@ -0,0 +1,91 @@
+#include "otd.h"
+#include "event.h"
+#include "drm.h"
+#include "udev.h"
+
+#include <stdbool.h>
+#include <stdlib.h>
+#include <poll.h>
+
+static inline void event_swap(struct otd_event *a, struct otd_event *b)
+{
+	struct otd_event tmp = *a;
+	*a = *b;
+	*b = tmp;
+}
+
+bool otd_get_event(struct otd *otd, struct otd_event *restrict ret)
+{
+	struct pollfd fds[] = {
+		{ .fd = otd->fd, .events = POLLIN },
+		{ .fd = otd->udev_fd, .events = POLLIN },
+	};
+
+	while (poll(fds, 2, 0) > 0) {
+		if (fds[0].revents)
+			get_drm_event(otd);
+		if (fds[1].revents)
+			otd_udev_event(otd);
+	}
+
+	if (otd->event_len == 0) {
+		ret->type = OTD_EV_NONE;
+		ret->display = NULL;
+		return false;
+	}
+
+	struct otd_event *ev = otd->events;
+
+	// Downheap
+	*ret = ev[0];
+	ev[0] = ev[--otd->event_len];
+
+	size_t i = 0;
+	while (i < otd->event_len / 2) {
+		size_t left = i * 2 + 1;
+		size_t right = i * 2 + 2;
+		size_t max = (ev[left].type > ev[right].type) ? left : right;
+
+		if (ev[i].type <= ev[max].type) {
+			event_swap(&ev[i], &ev[max]);
+			i = max;
+		} else {
+			break;
+		}
+	}
+
+	return true;
+}
+
+bool event_add(struct otd *otd, struct otd_display *disp, enum otd_event_type type)
+{
+	if (type == OTD_EV_NONE)
+		return true;
+
+	if (otd->event_len == otd->event_cap) {
+		size_t new_size = (otd->event_cap == 0) ? 8 : otd->event_cap * 2;
+
+		struct otd_event *new = realloc(otd->events, sizeof *new * new_size);
+		if (!new) {
+			return false;
+		}
+
+		otd->event_cap = new_size;
+		otd->events = new;
+	}
+
+	struct otd_event *ev = otd->events;
+
+	// Upheap
+	size_t i = otd->event_len++;
+	ev[i].type = type;
+	ev[i].display = disp;
+
+	size_t j;
+	while (i > 0 && ev[i].type > ev[(j = (i - 1) / 2)].type) {
+		event_swap(&ev[i], &ev[j]);
+		i = j;
+	}
+
+	return true;
+}

backend/drm/event.h

@@ -0,0 +1,21 @@
+#ifndef EVENT_H
+#define EVENT_H
+
+#include <stdbool.h>
+
+enum otd_event_type {
+	OTD_EV_NONE,
+	OTD_EV_RENDER,
+	OTD_EV_DISPLAY_REM,
+	OTD_EV_DISPLAY_ADD,
+};
+
+struct otd_event {
+	enum otd_event_type type;
+	struct otd_display *display;
+};
+
+bool otd_get_event(struct otd *otd, struct otd_event *restrict ret);
+bool event_add(struct otd *otd, struct otd_display *disp, enum otd_event_type type);
+
+#endif

backend/drm/main.c

@@ -0,0 +1,160 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include <inttypes.h>
+#include <time.h>
+#include <GLES3/gl3.h>
+#include <unistd.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdnoreturn.h>
+
+#include "otd.h"
+#include "drm.h"
+#include "event.h"
+
+// I know this is pretty crappy,
+// but it's just for the example's sake
+struct {
+	char *name;
+	char *mode;
+} displays[8];
+int num_displays = 0;
+
+noreturn void usage(const char *name, int ret)
+{
+	fprintf(stderr, "usage: %s [-o <name> [-m <mode>]]*\n"
+			"\n"
+			"  -h       \tDisplay this help text\n"
+			"  -o <name>\tWhich diplay to use. e.g. DVI-I-1.\n"
+			"  -m <mode>\tWhich mode to use. It must come after an -o option.\n"
+			"           \tMust be either 'preferred', 'current', widthxheight\n"
+			"           \tor widthxheight@rate. Defaults to 'preferred'.\n"
+			"\n"
+			"example: %s -o DVI-I-1 -m 1920x1080@60 -o DP-1 -m 1920x1200\n",
+			name, name);
+
+	exit(ret);
+}
+
+void parse_args(int argc, char *argv[])
+{
+	int c;
+	int i = -1;
+
+	while ((c = getopt(argc, argv, "ho:m:")) != -1) {
+		switch (c) {
+		case 'h':
+			usage(argv[0], 0);
+		case 'o':
+			i = num_displays++;
+
+			if (num_displays == 8) {
+				fprintf(stderr, "Too many displays\n");
+				exit(1);
+			}
+
+			displays[i].name = strdup(optarg);
+			break;
+		case 'm':
+			if (i == -1) {
+				fprintf(stderr, "A display is required first\n");
+				exit(1);
+			}
+
+			fprintf(stderr, "Assigned '%s' to '%s'\n", optarg, displays[i].name);
+			displays[i].mode = optarg;
+			i = -1;
+			break;
+		default:
+			usage(argv[0], 1);
+		}
+	}
+
+	// Trailing args
+	if (optind != argc) {
+		usage(argv[0], 1);
+	}
+}
+
+int main(int argc, char *argv[])
+{
+	parse_args(argc, argv);
+
+	struct otd *otd = otd_start();
+	if (!otd)
+		return 1;
+
+	float colour[3] = {1.0, 0.0, 0.0};
+	int dec = 0;
+
+	struct timespec start, now;
+	clock_gettime(CLOCK_MONOTONIC, &start);
+	struct timespec last = start;
+
+	while (clock_gettime(CLOCK_MONOTONIC, &now) == 0 &&
+	       now.tv_sec < start.tv_sec + 10) {
+
+		struct otd_event ev;
+		if (!otd_get_event(otd, &ev))
+			continue;
+
+		struct otd_display *disp = ev.display;
+
+		switch (ev.type) {
+		case OTD_EV_RENDER:
+			rendering_begin(disp);
+
+			// This is all just calculating the colours.
+			// It's not particularly important.
+
+			long ms = (now.tv_sec - last.tv_sec) * 1000 +
+				(now.tv_nsec - last.tv_nsec) / 1000000;
+
+			int inc = (dec + 1) % 3;
+
+			colour[dec] -= ms / 2000.0f;
+			colour[inc] += ms / 2000.0f;
+
+			if (colour[dec] < 0.0f) {
+				colour[dec] = 0.0f;
+				colour[inc] = 1.0f;
+
+				dec = (dec + 1) % 3;
+			}
+
+			last = now;
+
+			glViewport(0, 0, disp->width, disp->height);
+			glClearColor(colour[0], colour[1], colour[2], 1.0f);
+			glClear(GL_COLOR_BUFFER_BIT);
+
+			rendering_end(disp);
+			break;
+		case OTD_EV_DISPLAY_REM:
+			printf("%s removed\n", disp->name);
+			break;
+		case OTD_EV_DISPLAY_ADD:
+			printf("%s added\n", disp->name);
+
+			const char *mode = NULL;
+			for (int i = 0; i < num_displays; ++i) {
+				if (strcmp(disp->name, displays[i].name) == 0) {
+					mode = displays[i].mode;
+				}
+			}
+			if (!mode)
+				mode = "preferred";
+
+			if (!modeset_str(otd, ev.display, mode)) {
+				fprintf(stderr, "Modesetting %s failed\n", disp->name);
+				goto out;
+			}
+			break;
+		default:
+			break;
+		}
+	}
+
+out:
+	otd_finish(otd);
+}

backend/drm/otd.c

@@ -0,0 +1,71 @@
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#include "otd.h"
+#include "drm.h"
+#include "event.h"
+#include "session.h"
+#include "udev.h"
+
+struct otd *otd_start(void)
+{
+	struct otd *otd = calloc(1, sizeof *otd);
+	if (!otd)
+		return NULL;
+
+	if (!otd_new_session(otd)) {
+		fprintf(stderr, "Could not create session\n");
+		goto error;
+	}
+
+	if (!otd_udev_start(otd)) {
+		fprintf(stderr, "Could not start udev\n");
+		goto error_session;
+	}
+
+	otd_udev_find_gpu(otd);
+	if (otd->fd == -1) {
+		fprintf(stderr, "Could not open GPU\n");
+		goto error_udev;
+	}
+
+	if (!init_renderer(otd)) {
+		fprintf(stderr, "Could not initalise renderer\n");
+		goto error_fd;
+	}
+
+	scan_connectors(otd);
+
+	return otd;
+
+error_fd:
+	release_device(otd, otd->fd);
+error_udev:
+	otd_udev_finish(otd);
+error_session:
+	otd_close_session(otd);
+error:
+	free(otd);
+	return NULL;
+}
+
+void otd_finish(struct otd *otd)
+{
+	if (!otd)
+		return;
+
+	for (size_t i = 0; i < otd->display_len; ++i) {
+		destroy_display_renderer(otd, &otd->displays[i]);
+	}
+
+	destroy_renderer(otd);
+	otd_close_session(otd);
+	otd_udev_finish(otd);
+
+	close(otd->fd);
+	free(otd->events);
+	free(otd->displays);
+	free(otd);
+}
+

backend/drm/otd.h

@@ -0,0 +1,44 @@
+#ifndef LIBOTD_H
+#define LIBOTD_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <EGL/egl.h>
+#include <gbm.h>
+#include <libudev.h>
+
+#include "session.h"
+
+struct otd {
+	int fd;
+	bool paused;
+
+	// Priority Queue (Max-heap)
+	size_t event_cap;
+	size_t event_len;
+	struct otd_event *events;
+
+	size_t display_len;
+	struct otd_display *displays;
+
+	uint32_t taken_crtcs;
+
+	struct gbm_device *gbm;
+	struct {
+		EGLDisplay disp;
+		EGLConfig conf;
+		EGLContext context;
+	} egl;
+
+	struct otd_session session;
+
+	struct udev *udev;
+	struct udev_monitor *mon;
+	int udev_fd;
+	char *drm_path;
+};
+
+struct otd *otd_start(void);
+void otd_finish(struct otd *otd);
+
+#endif

backend/drm/session.c

@@ -0,0 +1,224 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <systemd/sd-bus.h>
+#include <systemd/sd-login.h>
+#include <unistd.h>
+#include <sys/sysmacros.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "session.h"
+#include "otd.h"
+
+int take_device(struct otd *restrict otd,
+		       const char *restrict path,
+		       bool *restrict paused_out)
+{
+	int ret;
+	int fd = -1;
+	sd_bus_message *msg = NULL;
+	sd_bus_error error = SD_BUS_ERROR_NULL;
+	struct otd_session *s = &otd->session;
+
+	struct stat st;
+	if (stat(path, &st) < 0) {
+		fprintf(stderr, "Failed to stat '%s'\n", path);
+		return -1;
+	}
+
+	ret = sd_bus_call_method(s->bus,
+				 "org.freedesktop.login1",
+				 s->path,
+				 "org.freedesktop.login1.Session",
+				 "TakeDevice",
+				 &error, &msg,
+				 "uu", major(st.st_rdev), minor(st.st_rdev));
+	if (ret < 0) {
+		fprintf(stderr, "%s\n", error.message);
+		goto error;
+	}
+
+	int paused = 0;
+	ret = sd_bus_message_read(msg, "hb", &fd, &paused);
+	if (ret < 0) {
+		fprintf(stderr, "%s\n", strerror(-ret));
+		goto error;
+	}
+
+	// The original fd seem to be closed when the message is freed
+	// so we just clone it.
+	fd = fcntl(fd, F_DUPFD_CLOEXEC, 0);
+
+	if (paused_out)
+		*paused_out = paused;
+
+error:
+	sd_bus_error_free(&error);
+	sd_bus_message_unref(msg);
+	return fd;
+}
+
+void release_device(struct otd *otd, int fd)
+{
+	int ret;
+	sd_bus_message *msg = NULL;
+	sd_bus_error error = SD_BUS_ERROR_NULL;
+	struct otd_session *s = &otd->session;
+
+	struct stat st;
+	if (fstat(fd, &st) < 0) {
+		fprintf(stderr, "Could not stat fd %d\n", fd);
+		return;
+	}
+
+	ret = sd_bus_call_method(s->bus,
+				 "org.freedesktop.login1",
+				 s->path,
+				 "org.freedesktop.login1.Session",
+				 "ReleaseDevice",
+				 &error, &msg,
+				 "uu", major(st.st_rdev), minor(st.st_rdev));
+	if (ret < 0) {
+		/* Log something */;
+	}
+
+	sd_bus_error_free(&error);
+	sd_bus_message_unref(msg);
+}
+
+static bool session_activate(struct otd *otd)
+{
+	int ret;
+	sd_bus_message *msg = NULL;
+	sd_bus_error error = SD_BUS_ERROR_NULL;
+	struct otd_session *s = &otd->session;
+
+	ret = sd_bus_call_method(s->bus,
+				 "org.freedesktop.login1",
+				 s->path,
+				 "org.freedesktop.login1.Session",
+				 "Activate",
+				 &error, &msg,
+				 "");
+	if (ret < 0) {
+		fprintf(stderr, "%s\n", error.message);
+	}
+
+	sd_bus_error_free(&error);
+	sd_bus_message_unref(msg);
+	return ret >= 0;
+}
+
+static bool take_control(struct otd *otd)
+{
+	int ret;
+	sd_bus_message *msg = NULL;
+	sd_bus_error error = SD_BUS_ERROR_NULL;
+	struct otd_session *s = &otd->session;
+
+	ret = sd_bus_call_method(s->bus,
+				 "org.freedesktop.login1",
+				 s->path,
+				 "org.freedesktop.login1.Session",
+				 "TakeControl",
+				 &error, &msg,
+				 "b", false);
+	if (ret < 0) {
+		/* Log something */;
+	}
+
+	sd_bus_error_free(&error);
+	sd_bus_message_unref(msg);
+	return ret >= 0;
+}
+
+static void release_control(struct otd *otd)
+{
+	int ret;
+	sd_bus_message *msg = NULL;
+	sd_bus_error error = SD_BUS_ERROR_NULL;
+	struct otd_session *s = &otd->session;
+
+	ret = sd_bus_call_method(s->bus,
+				 "org.freedesktop.login1",
+				 s->path,
+				 "org.freedesktop.login1.Session",
+				 "ReleaseControl",
+				 &error, &msg,
+				 "");
+	if (ret < 0) {
+		/* Log something */;
+	}
+
+	sd_bus_error_free(&error);
+	sd_bus_message_unref(msg);
+}
+
+void otd_close_session(struct otd *otd)
+{
+	release_device(otd, otd->fd);
+	release_control(otd);
+
+	sd_bus_unref(otd->session.bus);
+	free(otd->session.id);
+	free(otd->session.path);
+	free(otd->session.seat);
+}
+
+bool otd_new_session(struct otd *otd)
+{
+	int ret;
+	struct otd_session *s = &otd->session;
+
+	ret = sd_pid_get_session(getpid(), &s->id);
+	if (ret < 0) {
+		fprintf(stderr, "Could not get session\n");
+		goto error;
+	}
+
+	ret = sd_session_get_seat(s->id, &s->seat);
+	if (ret < 0) {
+		fprintf(stderr, "Could not get seat\n");
+		goto error;
+	}
+
+	// This could be done using asprintf, but I don't want to define _GNU_SOURCE
+
+	const char *fmt = "/org/freedesktop/login1/session/%s";
+	int len = snprintf(NULL, 0, fmt, s->id);
+
+	s->path = malloc(len + 1);
+	if (!s->path)
+		goto error;
+
+	sprintf(s->path, fmt, s->id);
+
+	ret = sd_bus_open_system(&s->bus);
+	if (ret < 0) {
+		fprintf(stderr, "Could not open bus\n");
+		goto error;
+	}
+
+	if (!session_activate(otd)) {
+		fprintf(stderr, "Could not activate session\n");
+		goto error_bus;
+	}
+
+	if (!take_control(otd)) {
+		fprintf(stderr, "Could not take control of session\n");
+		goto error_bus;
+	}
+
+	return true;
+
+error_bus:
+	sd_bus_unref(s->bus);
+
+error:
+	free(s->path);
+	free(s->id);
+	free(s->seat);
+	return false;
+}

backend/drm/session.h

@@ -0,0 +1,25 @@
+#ifndef SESSION_H
+#define SESSION_H
+
+#include <systemd/sd-bus.h>
+#include <stdbool.h>
+
+struct otd_session {
+	char *id;
+	char *path;
+	char *seat;
+
+	sd_bus *bus;
+};
+
+struct otd;
+bool otd_new_session(struct otd *otd);
+void otd_close_session(struct otd *otd);
+
+int take_device(struct otd *restrict otd,
+		       const char *restrict path,
+		       bool *restrict paused_out);
+
+void release_device(struct otd *otd, int fd);
+
+#endif

backend/drm/udev.c

@@ -0,0 +1,158 @@
+#include <libudev.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <xf86drm.h>
+#include <xf86drmMode.h>
+
+#include "otd.h"
+#include "udev.h"
+#include "session.h"
+#include "drm.h"
+
+static bool device_is_kms(struct otd *otd, struct udev_device *dev)
+{
+	const char *path = udev_device_get_devnode(dev);
+	int fd;
+
+	if (!path)
+		return false;
+
+	fd = take_device(otd, path, &otd->paused);
+	if (fd < 0)
+		return false;
+
+	drmModeRes *res = drmModeGetResources(fd);
+	if (!res)
+		goto out_fd;
+
+	if (res->count_crtcs <= 0 || res->count_connectors <= 0 ||
+	    res->count_encoders <= 0)
+		goto out_res;
+
+	if (otd->fd >= 0) {
+		release_device(otd, otd->fd);
+		free(otd->drm_path);
+	}
+
+	otd->fd = fd;
+	otd->drm_path = strdup(path);
+
+	drmModeFreeResources(res);
+	return true;
+
+out_res:
+	drmModeFreeResources(res);
+out_fd:
+	release_device(otd, fd);
+	return false;
+}
+
+void otd_udev_find_gpu(struct otd *otd)
+{
+	struct udev *udev = otd->udev;
+	otd->fd = -1;
+
+	struct udev_enumerate *en = udev_enumerate_new(udev);
+	if (!en)
+		return;
+
+	udev_enumerate_add_match_subsystem(en, "drm");
+	udev_enumerate_add_match_sysname(en, "card[0-9]*");
+
+	udev_enumerate_scan_devices(en);
+	struct udev_list_entry *entry;
+	udev_list_entry_foreach(entry, udev_enumerate_get_list_entry(en)) {
+		bool is_boot_vga = false;
+
+		const char *path = udev_list_entry_get_name(entry);
+		struct udev_device *dev = udev_device_new_from_syspath(udev, path);
+		if (!dev)
+			continue;
+
+		const char *seat = udev_device_get_property_value(dev, "ID_SEAT");
+		if (!seat)
+			seat = "seat0";
+		if (strcmp(otd->session.seat, seat) != 0) {
+			udev_device_unref(dev);
+			continue;
+		}
+
+		struct udev_device *pci =
+			udev_device_get_parent_with_subsystem_devtype(dev,
+								      "pci", NULL);
+
+		if (pci) {
+			const char *id = udev_device_get_sysattr_value(pci, "boot_vga");
+			if (id && strcmp(id, "1") == 0)
+				is_boot_vga = true;
+			udev_device_unref(pci);
+		}
+
+		if (!is_boot_vga && otd->fd >= 0) {
+			udev_device_unref(dev);
+			continue;
+		}
+
+		if (!device_is_kms(otd, dev)) {
+			udev_device_unref(dev);
+			continue;
+		}
+
+		if (is_boot_vga) {
+			break;
+		}
+	}
+
+	udev_enumerate_unref(en);
+}
+
+bool otd_udev_start(struct otd *otd)
+{
+	otd->udev = udev_new();
+	if (!otd->udev)
+		return false;
+
+	otd->mon = udev_monitor_new_from_netlink(otd->udev, "udev");
+	if (!otd->mon) {
+		udev_unref(otd->udev);
+		return false;
+	}
+
+	udev_monitor_filter_add_match_subsystem_devtype(otd->mon, "drm", NULL);
+	udev_monitor_enable_receiving(otd->mon);
+
+	otd->udev_fd = udev_monitor_get_fd(otd->mon);
+
+	return true;
+}
+
+void otd_udev_finish(struct otd *otd)
+{
+	if (!otd)
+		return;
+
+	udev_monitor_unref(otd->mon);
+	udev_unref(otd->udev);
+}
+
+void otd_udev_event(struct otd *otd)
+{
+	struct udev_device *dev = udev_monitor_receive_device(otd->mon);
+	if (!dev)
+		return;
+
+	const char *path = udev_device_get_devnode(dev);
+	if (!path || strcmp(path, otd->drm_path) != 0)
+		goto out;
+
+	const char *action = udev_device_get_action(dev);
+	if (!action || strcmp(action, "change") != 0)
+		goto out;
+
+	scan_connectors(otd);
+
+out:
+	udev_device_unref(dev);
+}

backend/drm/udev.h

@@ -0,0 +1,9 @@
+#ifndef UDEV_H
+#define UDEV_H
+
+bool otd_udev_start(struct otd *otd);
+void otd_udev_finish(struct otd *otd);
+void otd_udev_find_gpu(struct otd *otd);
+void otd_udev_event(struct otd *otd);
+
+#endif