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dirty and small example of libdrm
/* please refer better example: https://github.com/dvdhrm/docs/tree/master/drm-howto/ */
#define _XOPEN_SOURCE 600
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <xf86drm.h>
#include <xf86drmMode.h>
static const char *dri_path = "/dev/dri/card0";
enum {
DEPTH = 24,
BPP = 32,
};
struct drm_dev_t {
uint32_t *buf;
uint32_t conn_id, enc_id, crtc_id, fb_id;
uint32_t width, height;
uint32_t pitch, size, handle;
drmModeModeInfo mode;
drmModeCrtc *saved_crtc;
struct drm_dev_t *next;
};
void fatal(char *str)
{
fprintf(stderr, "%s\n", str);
exit(EXIT_FAILURE);
}
void error(char *str)
{
perror(str);
exit(EXIT_FAILURE);
}
int eopen(const char *path, int flag)
{
int fd;
if ((fd = open(path, flag)) < 0) {
fprintf(stderr, "cannot open \"%s\"\n", path);
error("open");
}
return fd;
}
void *emmap(int addr, size_t len, int prot, int flag, int fd, off_t offset)
{
uint32_t *fp;
if ((fp = (uint32_t *) mmap(0, len, prot, flag, fd, offset)) == MAP_FAILED)
error("mmap");
return fp;
}
int drm_open(const char *path)
{
int fd, flags;
uint64_t has_dumb;
fd = eopen(path, O_RDWR);
/* set FD_CLOEXEC flag */
if ((flags = fcntl(fd, F_GETFD)) < 0
|| fcntl(fd, F_SETFD, flags | FD_CLOEXEC) < 0)
fatal("fcntl FD_CLOEXEC failed");
/* check capability */
if (drmGetCap(fd, DRM_CAP_DUMB_BUFFER, &has_dumb) < 0 || has_dumb == 0)
fatal("drmGetCap DRM_CAP_DUMB_BUFFER failed or doesn't have dumb buffer");
return fd;
}
struct drm_dev_t *drm_find_dev(int fd)
{
int i;
struct drm_dev_t *dev = NULL, *dev_head = NULL;
drmModeRes *res;
drmModeConnector *conn;
drmModeEncoder *enc;
if ((res = drmModeGetResources(fd)) == NULL)
fatal("drmModeGetResources() failed");
/* find all available connectors */
for (i = 0; i < res->count_connectors; i++) {
conn = drmModeGetConnector(fd, res->connectors[i]);
if (conn != NULL && conn->connection == DRM_MODE_CONNECTED && conn->count_modes > 0) {
dev = (struct drm_dev_t *) malloc(sizeof(struct drm_dev_t));
memset(dev, 0, sizeof(struct drm_dev_t));
dev->conn_id = conn->connector_id;
dev->enc_id = conn->encoder_id;
dev->next = NULL;
memcpy(&dev->mode, &conn->modes[0], sizeof(drmModeModeInfo));
dev->width = conn->modes[0].hdisplay;
dev->height = conn->modes[0].vdisplay;
/* FIXME: use default encoder/crtc pair */
if ((enc = drmModeGetEncoder(fd, dev->enc_id)) == NULL)
fatal("drmModeGetEncoder() faild");
dev->crtc_id = enc->crtc_id;
drmModeFreeEncoder(enc);
dev->saved_crtc = NULL;
/* create dev list */
dev->next = dev_head;
dev_head = dev;
}
drmModeFreeConnector(conn);
}
drmModeFreeResources(res);
return dev_head;
}
void drm_setup_fb(int fd, struct drm_dev_t *dev)
{
struct drm_mode_create_dumb creq;
struct drm_mode_map_dumb mreq;
memset(&creq, 0, sizeof(struct drm_mode_create_dumb));
creq.width = dev->width;
creq.height = dev->height;
creq.bpp = BPP; // hard conding
if (drmIoctl(fd, DRM_IOCTL_MODE_CREATE_DUMB, &creq) < 0)
fatal("drmIoctl DRM_IOCTL_MODE_CREATE_DUMB failed");
dev->pitch = creq.pitch;
dev->size = creq.size;
dev->handle = creq.handle;
if (drmModeAddFB(fd, dev->width, dev->height,
DEPTH, BPP, dev->pitch, dev->handle, &dev->fb_id))
fatal("drmModeAddFB failed");
memset(&mreq, 0, sizeof(struct drm_mode_map_dumb));
mreq.handle = dev->handle;
if (drmIoctl(fd, DRM_IOCTL_MODE_MAP_DUMB, &mreq))
fatal("drmIoctl DRM_IOCTL_MODE_MAP_DUMB failed");
dev->buf = (uint32_t *) emmap(0, dev->size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, mreq.offset);
dev->saved_crtc = drmModeGetCrtc(fd, dev->crtc_id); /* must store crtc data */
if (drmModeSetCrtc(fd, dev->crtc_id, dev->fb_id, 0, 0, &dev->conn_id, 1, &dev->mode))
fatal("drmModeSetCrtc() failed");
}
void drm_destroy(int fd, struct drm_dev_t *dev_head)
{
struct drm_dev_t *devp, *devp_tmp;
struct drm_mode_destroy_dumb dreq;
for (devp = dev_head; devp != NULL;) {
if (devp->saved_crtc)
drmModeSetCrtc(fd, devp->saved_crtc->crtc_id, devp->saved_crtc->buffer_id,
devp->saved_crtc->x, devp->saved_crtc->y, &devp->conn_id, 1, &devp->saved_crtc->mode);
drmModeFreeCrtc(devp->saved_crtc);
munmap(devp->buf, devp->size);
drmModeRmFB(fd, devp->fb_id);
memset(&dreq, 0, sizeof(dreq));
dreq.handle = devp->handle;
drmIoctl(fd, DRM_IOCTL_MODE_DESTROY_DUMB, &dreq);
devp_tmp = devp;
devp = devp->next;
free(devp_tmp);
}
close(fd);
}
int main()
{
int fd;
int i, j;
uint8_t color;
struct drm_dev_t *dev_head, *dev;
/* init */
fd = drm_open(dri_path);
dev_head = drm_find_dev(fd);
if (dev_head == NULL) {
fprintf(stderr, "available drm_dev not found\n");
return EXIT_FAILURE;
}
printf("available connector(s)\n\n");
for (dev = dev_head; dev != NULL; dev = dev->next) {
printf("connector id:%d\n", dev->conn_id);
printf("\tencoder id:%d crtc id:%d fb id:%d\n", dev->enc_id, dev->crtc_id, dev->fb_id);
printf("\twidth:%d height:%d\n", dev->width, dev->height);
}
/* FIXME: use first drm_dev */
dev = dev_head;
drm_setup_fb(fd, dev);
/* draw something */
for (i = 0; i < dev->height; i++)
for (j = 0; j < dev->width; j++) {
color = (double) (i * j) / (dev->height * dev->width) * 0xFF;
*(dev->buf + i * dev->width + j) = (uint32_t) 0xFFFFFF & (0x00 << 16 | color << 8 | color);
}
sleep(3);
/* destroy */
drm_destroy(fd, dev_head);
return 0;
}
@stefanalt
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stefanalt commented Dec 12, 2020

Nice. Almost certainly you need to fix the /* draw something */ body with something this:

*(dev->buf + i * (dev->pitch/(BPP/8)) + j) = (uint32_t) 0xFFFFFF & (0x00 << 16 | color << 8 | color);

Sometimes pitch != width !

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