qcam: viewfinder_gl: Render image centered in letterbox

Mimic the letterbox behaviour of the Qt viewfinder by rendering the
image centered. This is done by adding a projection matrix to the vertex
shader to scale the rendered rectangle.

Another option would have been to keep using glViewport() (which would
have needed to be moved to paintGL(), as Qt resets the viewport to span
the full widget before calling). Hidpi displays would then need special
handling of the device pixel ratio, which is done automatically by Qt
when it sets the default viewport. Using a projection matrix avoids this
complication.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

0 files changed, 0 insertions, 0 deletions