读取bmp图像用drm显示

要在DRM中显示BMP图像，您需要完成以下步骤：

1. 读取BMP图像数据：您可以使用任何BMP图像库或自己编写的代码来读取BMP图像的像素数据。

2. 创建DRM设备并打开设备：您需要使用DRM库来创建DRM设备并打开设备以进行渲染操作。

3. 创建DRM缓冲区：您需要使用DRM库来创建DRM缓冲区，这是您要将BMP图像数据复制到的内存区域。

4. 将BMP图像数据复制到DRM缓冲区：使用memcpy或类似的函数将BMP图像数据复制到DRM缓冲区。

5. 渲染DRM缓冲区：使用DRM库中的API将DRM缓冲区中的数据渲染到屏幕上。

下面是一个简单的代码示例，可以帮助您了解如何在DRM中显示BMP图像：

#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <unistd.h>

#include <drm/drm_fourcc.h>
#include <drm/drm_mode.h>
#include <xf86drm.h>

#define BUFFER_WIDTH 800
#define BUFFER_HEIGHT 600

int main(int argc, char **argv) {
  int fd = open("/dev/dri/card0", O_RDWR);
  if (fd < 0) {
    perror("failed to open DRM device");
    exit(EXIT_FAILURE);
  }

  drmModeRes *resources = drmModeGetResources(fd);
  if (!resources) {
    perror("failed to get DRM resources");
    close(fd);
    exit(EXIT_FAILURE);
  }

  drmModeConnector *connector = NULL;
  drmModeEncoder *encoder = NULL;
  for (int i = 0; i < resources->count_connectors; i++) {
    drmModeConnector *c = drmModeGetConnector(fd, resources->connectors[i]);
    if (c->connection == DRM_MODE_CONNECTED && c->count_modes > 0) {
      connector = c;
      break;
    }
    drmModeFreeConnector(c);
  }

  if (!connector) {
    perror("failed to find a connected DRM connector");
    drmModeFreeResources(resources);
    close(fd);
    exit(EXIT_FAILURE);
  }

  for (int i = 0; i < resources->count_encoders; i++) {
    drmModeEncoder *e = drmModeGetEncoder(fd, resources->encoders[i]);
    if (e->encoder_id == connector->encoder_id) {
      encoder = e;
      break;
    }
    drmModeFreeEncoder(e);
  }

  if (!encoder) {
    perror("failed to find a DRM encoder for the connector");
    drmModeFreeConnector(connector);
    drmModeFreeResources(resources);
    close(fd);
    exit(EXIT_FAILURE);
  }

  drmModeCrtc *crtc = drmModeGetCrtc(fd, encoder->crtc_id);
  if (!crtc) {
    perror("failed to get DRM CRTC");
    drmModeFreeEncoder(encoder);
    drmModeFreeConnector(connector);
    drmModeFreeResources(resources);
    close(fd);
    exit(EXIT_FAILURE);
  }

  uint32_t format = DRM_FORMAT_XRGB8888;
  uint32_t buffer_width = BUFFER_WIDTH;
  uint32_t buffer_height = BUFFER_HEIGHT;
  uint32_t pitch = buffer_width * 4;
  size_t buffer_size = pitch * buffer_height;

  uint32_t handle;
  uint32_t flags = 0;
  int ret = drmModeAddFB(fd, buffer_width, buffer_height, 24, 32, pitch, handle, &fb_id);
  if (ret) {
    perror("failed to add DRM framebuffer");
    drmModeFreeCrtc(crtc);
    drmModeFreeEncoder(encoder);
    drmModeFreeConnector(connector);
    drmModeFreeResources(resources);
    close(fd);
    exit(EXIT_FAILURE);
  }

  void *buffer = mmap(NULL, buffer_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, handle);
  if (buffer == MAP_FAILED) {
    perror("failed to mmap DRM buffer");
    drmModeRmFB(fd, fb_id);
    drmModeFreeCrtc(crtc);
    drmModeFreeEncoder(encoder);
    drmModeFreeConnector(connector);
    drmModeFreeResources(resources);
    close(fd);
    exit(EXIT_FAILURE);
  }

  // Read BMP image data into a buffer.
  FILE *fp = fopen("image.bmp", "rb");
  if (!fp) {
    perror("failed to open BMP image file");
    munmap(buffer, buffer_size);
    drmModeRmFB(fd, fb_id);
    drmModeFreeCrtc(crtc);
    drmModeFreeEncoder(encoder);
    drmModeFreeConnector(connector);
    drmModeFreeResources(resources);
    close(fd);
    exit(EXIT_FAILURE);
  }

  fseek(fp, 0L, SEEK_END);
  size_t bmp_size = ftell(fp);
  fseek(fp, 0L, SEEK_SET);

  uint8_t *bmp_data = malloc(bmp_size);
  fread(bmp_data, bmp_size, 1, fp);
  fclose(fp);

  // Copy BMP image data to the DRM buffer.
  uint8_t *dst = buffer;
  uint8_t *src = bmp_data + 54; // Skip BMP header.
  for (int y = 0; y < buffer_height; y++) {
    memcpy(dst, src, pitch);
    dst += pitch;
    src += buffer_width * 3; // BMP is stored BGR, so we skip 3 bytes per pixel.
  }

  free(bmp_data);

  // Render the DRM buffer to the screen.
  drmModeSetCrtc(fd, crtc->crtc_id, fb_id, 0, 0, &connector->connector_id, 1, &crtc->mode);
  drmModePageFlip(fd, crtc->crtc_id, fb_id, DRM_MODE_PAGE_FLIP_EVENT, NULL);

  // Wait for page flip event before exiting.
  fd_set fds;
  FD_ZERO(&fds);
  FD_SET(fd, &fds);

  while (true) {
    ret = select(fd + 1, &fds, NULL, NULL, NULL);
    if (ret < 0) {
      perror("failed to wait for DRM page flip event");
      break;
    } else if (ret == 0) {
      continue;
    } else {
      drmEventContext evctx = {
        .version = DRM_EVENT_CONTEXT_VERSION,
        .page_flip_handler = NULL,
      };
      drmHandleEvent(fd, &evctx);
      break;
    }
  }

  munmap(buffer, buffer_size);
  drmModeRmFB(fd, fb_id);
  drmModeFreeCrtc(crtc);
  drmModeFreeEncoder(encoder);
  drmModeFreeConnector(connector);
  drmModeFreeResources(resources);
  close(fd);

  return 0;
}

该代码示例假定您已经安装了DRM库并具有适当的开发环境。