[GEM-dev] pix_crop y coordinates

Matteo Sisti Sette matteosistisette at gmail.com
Thu Mar 18 16:23:06 CET 2010


IOhannes m zmoelnig escribió:
> On 2010-03-17 22:22, Matteo Sisti Sette wrote:
>> Hi,
>>
>> I'm realising that pix_crop x/y coordinates work as follows:
>>
>> - x grows from left to right
>> - y grows from bottom to top
>>
>> Isn't it a bit weird (the y part)? I know coordinate systems are always
>> arbitrary but, aren't digital images rows almost universally counted
>> from top to bottom? Isn't that even how they are stored in image files
>> and memory?
> 
> no. in openGL pixes are bottom up.

Oh, I see. Thank you


By the way (and somewhat unrelated), I have to do some serious test as 
soon as I have the occasion to use a Mac, but I have noticed 
inconsistencies in the ways things work between PC and Mac when using 
shaders.

That is, using the same patch with the same shaders (and both with 
rectanguar texture mode explicitly set, or explicitly turned off), I get 
an image or video correctly displayed on PC and upside-down in Mac (or, 
obviously, viceversa).

Does the OpenGL standard allow for some differencies between 
implementations in the way texture coordinates are treated, or is it 
safe to state that if the same patch with the same shaders gives 
different results (such as an image upside-down in either but not both) 
something is wrong in Gem?

thanks
m.


-- 
Matteo Sisti Sette
matteosistisette at gmail.com
http://www.matteosistisette.com




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