Picture magnification lag

[gadesx]

Detected a bug that decrease the FPS a lot:

Map without pictures: 60FPS
Map with a picture with 50 of magnification: 60FPS
Map with a picture with 100 of magnification: 60FPS
Map with a picture with 120 of magnification: 17FPS
Map with a picture with 200 of magnification: 7FPS
Map with a picture with 300 of magnification: 3FPS

I've tested the map with ID 5 from:
http://dl.dropboxusercontent.com/u/22524283/rpg%20maker/EASYRPG%20TESTER%203.rar
And I get magnification issues with 200% zoom as reported. The picture is big (2400x2400) and the blending operation might being done including offscreen data instead of clipped one.
There is more than 1 picture with partial opacity loaded in this test (needs multiple blending operations).

Confirmed, after making the image smaller (640x640) performance goes up (57-58 FPS).
A possible solution may be clipping visible image before running blitting operations.