Created attachment 171037 [details] [review]
Manage ratio for each texture in gloverlay

Fixes the following bugs:
  * the video and the image textures could not be positioned in the whole opengl window
  * allows changing the rendering's ratio without original textures deformation (both video and overlay image) by forcing their ratio

The 2 bugs are linked to the addition of original opengl caps usage, therefore the unified patch.

About textures positioning
=========================

Textures positioning calculations were originally based on the overlay image's original size, whereas now it uses the real opengl caps's width and height. 

Example issue (before patch): with an 1024x768 png overlay and 1280x720 input video resolution, when xpos-png=100 the overlay texture was not positioned at the right of the rendering.

About ratios
============

The opengl window's dimensions are the video texture's, thus preventing changing the rendering's ratio without deforming the video texture itself. The patch adds:
* a ratio-video property which forces back the video texture's ratio in the opengl rendering; supported values are: original, 4:3, 16:9, 16:10
* overlay image ratio conservation by using the original file's ratio

Example usage, where the file.mkv original ratio is 4:3 :

gst-launch filesrc location=file.mkv ! decodebin ! ffmpegcolorspace ! videorate ! videoscale ! "video/x-raw-yuv, format=(fourcc)I420, framerate=(fraction)25/1, pixel-aspect-ratio=(fraction)1/1, width=(int)1280, height=(int)720"  ! glupload ! gloverlay location=test.png proportion-png=50 xpos-png=100 ypos-png=100 proportion-video=50 xpos-video=0 ypos-video=100 ratio-video=1 video-top=true ! glimagesink

The trick is that the caps allow to modify the opengl window's dimensions to 1280x720, and the ratio-video property reverts the ratio changes by resizing the texture inside the rendering back to the specified ratio.