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@Miouyouyou
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An example, inspired by Rob Clark "kmscube.c" that uses Linux Direct Rendering Manager ( DRM ) and EGL to create an OpenGL ES 2 context. This is a standalone example, that just clears the screen with a blueish color. Usable with Rockchip DRM drivers and Mali Wayland/DRM userspace drivers.
// gcc -o drmgl Linux_DRM_OpenGLES.c `pkg-config --cflags --libs libdrm` -lgbm -lEGL -lGLESv2
/*
* Copyright (c) 2012 Arvin Schnell <arvin.schnell@gmail.com>
* Copyright (c) 2012 Rob Clark <rob@ti.com>
* Copyright (c) 2017 Miouyouyou <Myy> <myy@miouyouyou.fr>
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sub license,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the
* next paragraph) shall be included in all copies or substantial portions
* of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*/
/* Based on a egl cube test app originally written by Arvin Schnell */
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <xf86drm.h>
#include <xf86drmMode.h>
#include <gbm.h>
#define GL_GLEXT_PROTOTYPES 1
#include <GLES2/gl2.h>
#include <GLES2/gl2ext.h>
#include <EGL/egl.h>
#include <EGL/eglext.h>
#include <assert.h>
#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
static struct {
EGLDisplay display;
EGLConfig config;
EGLContext context;
EGLSurface surface;
GLuint program;
GLint modelviewmatrix, modelviewprojectionmatrix, normalmatrix;
GLuint vbo;
GLuint positionsoffset, colorsoffset, normalsoffset;
} gl;
static struct {
struct gbm_device *dev;
struct gbm_surface *surface;
} gbm;
static struct {
int fd;
drmModeModeInfo *mode;
uint32_t crtc_id;
uint32_t connector_id;
} drm;
struct drm_fb {
struct gbm_bo *bo;
uint32_t fb_id;
};
static uint32_t find_crtc_for_encoder(const drmModeRes *resources,
const drmModeEncoder *encoder) {
int i;
for (i = 0; i < resources->count_crtcs; i++) {
/* possible_crtcs is a bitmask as described here:
* https://dvdhrm.wordpress.com/2012/09/13/linux-drm-mode-setting-api
*/
const uint32_t crtc_mask = 1 << i;
const uint32_t crtc_id = resources->crtcs[i];
if (encoder->possible_crtcs & crtc_mask) {
return crtc_id;
}
}
/* no match found */
return -1;
}
static uint32_t find_crtc_for_connector(const drmModeRes *resources,
const drmModeConnector *connector) {
int i;
for (i = 0; i < connector->count_encoders; i++) {
const uint32_t encoder_id = connector->encoders[i];
drmModeEncoder *encoder = drmModeGetEncoder(drm.fd, encoder_id);
if (encoder) {
const uint32_t crtc_id = find_crtc_for_encoder(resources, encoder);
drmModeFreeEncoder(encoder);
if (crtc_id != 0) {
return crtc_id;
}
}
}
/* no match found */
return -1;
}
static int init_drm(void)
{
drmModeRes *resources;
drmModeConnector *connector = NULL;
drmModeEncoder *encoder = NULL;
int i, area;
drm.fd = open("/dev/dri/card0", O_RDWR);
if (drm.fd < 0) {
printf("could not open drm device\n");
return -1;
}
resources = drmModeGetResources(drm.fd);
if (!resources) {
printf("drmModeGetResources failed: %s\n", strerror(errno));
return -1;
}
/* find a connected connector: */
for (i = 0; i < resources->count_connectors; i++) {
connector = drmModeGetConnector(drm.fd, resources->connectors[i]);
if (connector->connection == DRM_MODE_CONNECTED) {
/* it's connected, let's use this! */
break;
}
drmModeFreeConnector(connector);
connector = NULL;
}
if (!connector) {
/* we could be fancy and listen for hotplug events and wait for
* a connector..
*/
printf("no connected connector!\n");
return -1;
}
/* find prefered mode or the highest resolution mode: */
for (i = 0, area = 0; i < connector->count_modes; i++) {
drmModeModeInfo *current_mode = &connector->modes[i];
if (current_mode->type & DRM_MODE_TYPE_PREFERRED) {
drm.mode = current_mode;
}
int current_area = current_mode->hdisplay * current_mode->vdisplay;
if (current_area > area) {
drm.mode = current_mode;
area = current_area;
}
}
if (!drm.mode) {
printf("could not find mode!\n");
return -1;
}
/* find encoder: */
for (i = 0; i < resources->count_encoders; i++) {
encoder = drmModeGetEncoder(drm.fd, resources->encoders[i]);
if (encoder->encoder_id == connector->encoder_id)
break;
drmModeFreeEncoder(encoder);
encoder = NULL;
}
if (encoder) {
drm.crtc_id = encoder->crtc_id;
} else {
uint32_t crtc_id = find_crtc_for_connector(resources, connector);
if (crtc_id == 0) {
printf("no crtc found!\n");
return -1;
}
drm.crtc_id = crtc_id;
}
drm.connector_id = connector->connector_id;
return 0;
}
static int init_gbm(void)
{
gbm.dev = gbm_create_device(drm.fd);
gbm.surface = gbm_surface_create(gbm.dev,
drm.mode->hdisplay, drm.mode->vdisplay,
GBM_FORMAT_XRGB8888,
GBM_BO_USE_SCANOUT | GBM_BO_USE_RENDERING);
if (!gbm.surface) {
printf("failed to create gbm surface\n");
return -1;
}
return 0;
}
static int init_gl(void)
{
EGLint major, minor, n;
GLuint vertex_shader, fragment_shader;
GLint ret;
static const EGLint context_attribs[] = {
EGL_CONTEXT_CLIENT_VERSION, 2,
EGL_NONE
};
static const EGLint config_attribs[] = {
EGL_SURFACE_TYPE, EGL_WINDOW_BIT,
EGL_RED_SIZE, 1,
EGL_GREEN_SIZE, 1,
EGL_BLUE_SIZE, 1,
EGL_ALPHA_SIZE, 0,
EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
EGL_NONE
};
PFNEGLGETPLATFORMDISPLAYEXTPROC get_platform_display = NULL;
get_platform_display =
(void *) eglGetProcAddress("eglGetPlatformDisplayEXT");
assert(get_platform_display != NULL);
gl.display = get_platform_display(EGL_PLATFORM_GBM_KHR, gbm.dev, NULL);
if (!eglInitialize(gl.display, &major, &minor)) {
printf("failed to initialize\n");
return -1;
}
printf("Using display %p with EGL version %d.%d\n",
gl.display, major, minor);
printf("EGL Version \"%s\"\n", eglQueryString(gl.display, EGL_VERSION));
printf("EGL Vendor \"%s\"\n", eglQueryString(gl.display, EGL_VENDOR));
printf("EGL Extensions \"%s\"\n", eglQueryString(gl.display, EGL_EXTENSIONS));
if (!eglBindAPI(EGL_OPENGL_ES_API)) {
printf("failed to bind api EGL_OPENGL_ES_API\n");
return -1;
}
if (!eglChooseConfig(gl.display, config_attribs, &gl.config, 1, &n) || n != 1) {
printf("failed to choose config: %d\n", n);
return -1;
}
gl.context = eglCreateContext(gl.display, gl.config,
EGL_NO_CONTEXT, context_attribs);
if (gl.context == NULL) {
printf("failed to create context\n");
return -1;
}
gl.surface = eglCreateWindowSurface(gl.display, gl.config, gbm.surface, NULL);
if (gl.surface == EGL_NO_SURFACE) {
printf("failed to create egl surface\n");
return -1;
}
/* connect the context to the surface */
eglMakeCurrent(gl.display, gl.surface, gl.surface, gl.context);
printf("GL Extensions: \"%s\"\n", glGetString(GL_EXTENSIONS));
return 0;
}
/* Draw code here */
static void draw(uint32_t i)
{
glClear(GL_COLOR_BUFFER_BIT);
glClearColor(0.2f, 0.3f, 0.5f, 1.0f);
}
static void
drm_fb_destroy_callback(struct gbm_bo *bo, void *data)
{
struct drm_fb *fb = data;
struct gbm_device *gbm = gbm_bo_get_device(bo);
if (fb->fb_id)
drmModeRmFB(drm.fd, fb->fb_id);
free(fb);
}
static struct drm_fb * drm_fb_get_from_bo(struct gbm_bo *bo)
{
struct drm_fb *fb = gbm_bo_get_user_data(bo);
uint32_t width, height, stride, handle;
int ret;
if (fb)
return fb;
fb = calloc(1, sizeof *fb);
fb->bo = bo;
width = gbm_bo_get_width(bo);
height = gbm_bo_get_height(bo);
stride = gbm_bo_get_stride(bo);
handle = gbm_bo_get_handle(bo).u32;
ret = drmModeAddFB(drm.fd, width, height, 24, 32, stride, handle, &fb->fb_id);
if (ret) {
printf("failed to create fb: %s\n", strerror(errno));
free(fb);
return NULL;
}
gbm_bo_set_user_data(bo, fb, drm_fb_destroy_callback);
return fb;
}
static void page_flip_handler(int fd, unsigned int frame,
unsigned int sec, unsigned int usec, void *data)
{
int *waiting_for_flip = data;
*waiting_for_flip = 0;
}
int main(int argc, char *argv[])
{
fd_set fds;
drmEventContext evctx = {
.version = DRM_EVENT_CONTEXT_VERSION,
.page_flip_handler = page_flip_handler,
};
struct gbm_bo *bo;
struct drm_fb *fb;
uint32_t i = 0;
int ret;
ret = init_drm();
if (ret) {
printf("failed to initialize DRM\n");
return ret;
}
FD_ZERO(&fds);
FD_SET(0, &fds);
FD_SET(drm.fd, &fds);
ret = init_gbm();
if (ret) {
printf("failed to initialize GBM\n");
return ret;
}
ret = init_gl();
if (ret) {
printf("failed to initialize EGL\n");
return ret;
}
/* clear the color buffer */
glClearColor(0.5, 0.5, 0.5, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
eglSwapBuffers(gl.display, gl.surface);
bo = gbm_surface_lock_front_buffer(gbm.surface);
fb = drm_fb_get_from_bo(bo);
/* set mode: */
ret = drmModeSetCrtc(drm.fd, drm.crtc_id, fb->fb_id, 0, 0,
&drm.connector_id, 1, drm.mode);
if (ret) {
printf("failed to set mode: %s\n", strerror(errno));
return ret;
}
while (1) {
struct gbm_bo *next_bo;
int waiting_for_flip = 1;
draw(i++);
eglSwapBuffers(gl.display, gl.surface);
next_bo = gbm_surface_lock_front_buffer(gbm.surface);
fb = drm_fb_get_from_bo(next_bo);
/*
* Here you could also update drm plane layers if you want
* hw composition
*/
ret = drmModePageFlip(drm.fd, drm.crtc_id, fb->fb_id,
DRM_MODE_PAGE_FLIP_EVENT, &waiting_for_flip);
if (ret) {
printf("failed to queue page flip: %s\n", strerror(errno));
return -1;
}
while (waiting_for_flip) {
ret = select(drm.fd + 1, &fds, NULL, NULL, NULL);
if (ret < 0) {
printf("select err: %s\n", strerror(errno));
return ret;
} else if (ret == 0) {
printf("select timeout!\n");
return -1;
} else if (FD_ISSET(0, &fds)) {
printf("user interrupted!\n");
break;
}
drmHandleEvent(drm.fd, &evctx);
}
/* release last buffer to render on again: */
gbm_surface_release_buffer(gbm.surface, bo);
bo = next_bo;
}
return ret;
}
@Miouyouyou
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Thanks for the heads-up !

Turns out that I'm receiving the comments to the Gist now. This seems to have changed... 6 months ago I guess ?

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