can we display same framebuffer side by side on screen simultaneously using DRM(direct rendering manager) APIs in linux?

Question

can we display same framebuffer side by side on screen simultaneously using DRM(direct rendering manager) APIs in linux?

---

constraints:

• need to use single plane and single framebuffer

what I already tried and failed:

• i used two setplane calls for left and right halves of screen respectively in a single vblank.
• in the above case the second setplane call was resetting the left half of screen. hence only right half is being displayed finally.

resolutions: framebuffer: 1920 * 1080 screen: 3840 * 2160

Answer 1

To implement side-by-side framebuffer display using Linux's DRM API, it is necessary to:

• create and configure framebuffers
• interact with DRM to acess graphics hardware
• set up and position planes for each framebuffer segment
• manage scaling and refresh operations

Here's my example:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <xf86drm.h>
#include <xf86drmMode.h>

int main(int argc, char **argv) {
    int fd = drmOpen("i915", NULL); // Replace "i915" with your GPU driver
    if (fd < 0) {
        perror("drmOpen");
        return 1;
    }

    drmModeRes *res = drmModeGetResources(fd);
    if (!res) {
        perror("drmModeGetResources");
        drmClose(fd);
        return 1;
    }

    // Assuming the first connected connector and its encoder and CRTC
    drmModeConnector *connector = drmModeGetConnector(fd, res->connectors[0]);
    drmModeEncoder *encoder = drmModeGetEncoder(fd, connector->encoder_id);
    drmModeCrtc *orig_crtc = drmModeGetCrtc(fd, encoder->crtc_id);

    uint32_t buffer_id;
    // Assume a framebuffer is already created and filled with data, use its ID here
    buffer_id = YOUR_FRAMEBUFFER_ID;

    // Display the buffer in two parts side by side
    for (int i = 0; i < 2; i++) {
        drmModeSetPlane(fd, res->planes[i], orig_crtc->crtc_id, buffer_id, 0,
                        1920 * i, 0, 1920, 1080,   // Destination rectangle
                        0, 0, 1920 << 16, 1080 << 16);  // Source rectangle (fixed-point format)
    }

    // Main loop or further processing
    printf("Framebuffers displayed side by side.\n");

    // Clean up resources
    drmModeFreeCrtc(orig_crtc);
    drmModeFreeEncoder(encoder);
    drmModeFreeConnector(connector);
    drmModeFreeResources(res);
    drmClose(fd);

    return 0;
}