Unsupported format HAL_PIXEL_FORMAT_YCbCr_420_888

[goffioul]

On Android R (android-11.0.0_r35) with mesa-21.1.0, gbm_gralloc and drm_hwcomposer, opening the webcam in a WebView (Chrome/89) crashes the app at this line: https://github.com/robherring/gbm_gralloc/blob/master/gralloc_gbm.cpp#L386

The format requested is HAL_PIXEL_FORMAT_YCbCr_420_888 (35), which is not supported by gralloc_gbm_get_bpp. It returns 0 and leads to SIGFPE.

[goffioul]

After finding various references about mapping the flexible pixel format to NV12, I tried this patch, which seems to solve the problem on my Baytrail platform, there's no crash and the WebView is able to access/display the webcam stream:

diff --git a/gralloc_gbm.cpp b/gralloc_gbm.cpp
index 5670213..75043dd 100644
--- a/gralloc_gbm.cpp
+++ b/gralloc_gbm.cpp
@@ -98,6 +98,7 @@ static uint32_t get_gbm_format(int format)
                break;
        case HAL_PIXEL_FORMAT_YCbCr_422_SP:
        case HAL_PIXEL_FORMAT_YCrCb_420_SP:
+       case HAL_PIXEL_FORMAT_YCbCr_420_888:
        default:
                fmt = 0;
                break;
@@ -127,6 +128,7 @@ static int gralloc_gbm_get_bpp(int format)
        case HAL_PIXEL_FORMAT_YV12:
        case HAL_PIXEL_FORMAT_YCbCr_422_SP:
        case HAL_PIXEL_FORMAT_YCrCb_420_SP:
+       case HAL_PIXEL_FORMAT_YCbCr_420_888:
                bpp = 1;
                break;
        default:
@@ -507,6 +509,7 @@ int gralloc_gbm_bo_lock_ycbcr(buffer_handle_t handle,
 
        switch (hnd->format) {
        case HAL_PIXEL_FORMAT_YCrCb_420_SP:
+       case HAL_PIXEL_FORMAT_YCbCr_420_888:
                ystride = cstride = GRALLOC_ALIGN(hnd->width, 16);
                ycbcr->y = addr;
                ycbcr->cr = (unsigned char *)addr + ystride * hnd->height;