[Bf-taskforce25] Silly note about area/region/mask sizes vs. matrices

[Ton Roosendaal]

Hi,

To keep the Blender UI behaving nice stable, it's important to keep 
track of this issue:

Rects for area, region, and view2d masks are in pixel coordinates. 
They're integers, and use coordinates from start-pixel to (and 
including) the end-pixel.
Example: a region rect (100, 100, 200, 200) is actually of "size" (101, 
101). A similar sized region or mask above that should get coordinates 
(100, 201, 200, 301).

This is how glViewport then should be set:

	/* glViewport(x, y, sizex, sizey); */
	glViewport(xmin, ymin, xmax-xmin+1, ymax-ymin+1);

Same goes for a 1:1 mapping for drawing:

	wmOrtho2(C->window, 0, 101, 0, 101);

The opengl spec defines that you should substract 0.375 from the above 
values for 100% accurate 1:1 mapped transform.

I've noticed some glitches for this in my code, which is being 
submitted now. :)

-Ton-

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Ton Roosendaal  Blender Foundation   ton at blender.org    www.blender.org
Blender Institute BV  Entrepotdok 57A  1018AD Amsterdam The Netherlands