DISPMANX_MODEINFO_T transform value sometimes correct

[waveform80]

I've been working on adding screenshot capabilities to picamera and ran across something a little odd in the result of vc_dispmanx_display_get_info. When display_rotate (in /boot/config.txt) is set to 0, 1, or 3 (no rotation, 90 degrees, or 270 degrees), the info returned by vc_dispmanx_display_get_info is as expected: width and height are all correct (swapped in the case of 90 or 270 degree rotation), and the transform field reports the display rotation (0, 1, or 3).

However, when display_rotate is set to 2 (180 degree rotation), width and height are correct (same as unrotated), but transform reads 0 (the display is definitely rotated though). The same happens for 65536 and 131072 (horizontal and vertical flip) too, but I'm not sure if those are documented use-cases.

The following little snippet of C should demonstrate things:

#include <stdio.h>
#include "bcm_host.h"

int main(void) {
    DISPMANX_DISPLAY_HANDLE_T display;
    DISPMANX_MODEINFO_T info;

    bcm_host_init();
    display = vc_dispmanx_display_open(0);
    vc_dispmanx_display_get_info(display, &info);
    printf("Size: %dx%d, Transform: %d\n", info.width, info.height, info.transform);
}

[popcornmix]

Are you happy just getting the value of display_rotate back?
i.e. 0, 1, 2, 3 for standard rotations with 65536 or 131072 added if there are flips?

[waveform80]

Yup, that'd be perfect.

I've had a look at raspi2png's source code while I'm at it and it seems to work around the issue by using vc_gencmd to query the display_rotate parameter directly. I haven't translated that header yet, so this getting fixed might save me a bit of work (and from the looks of it, vc_gencmd involves some string parsing under the covers - always nice to avoid stuff like that if possible :).

[popcornmix]

Test firmware you can try: https://www.dropbox.com/s/oo5f4ztfozgeg06/firmware_ip.zip?dl=0

[waveform80]

Many thanks - that works nicely!

[JamesH65]

@popcornmix Did this get merged?

[popcornmix]

Yes (you can see the firmware updates that link to this issue above)

[JamesH65]

Cool, closing.