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.

IOhannes m zmoelnig escribió:

it's a known issue. until this is fixed (i almost got it there, remember the thread on having to premultiply texture transformation matrices in shaders?),

Oh, I'll look for that thread and have a look.

thanks m.

On 2010-03-18 16:55, Matteo Sisti Sette wrote:

By the way, it is not in the bug tracker, is it?

Something related is mentioned in bug 2844089 but that is specific to [model] and the bug itself doesn't seem to be the consequence of the issue we're talking about here.......

it is (unless i am mistaken)

fgmasdr IOhannes

On Thu, Mar 18, 2010 at 11:23 AM, Matteo Sisti Sette < matteosistisette@gmail.com> wrote:

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?

OpenGL absolutely allows for platform specific behavior, and programmers have to account for those. This includes writing different shaders for different platforms!

On 2010-03-18 17:35, Matteo Sisti Sette wrote:

chris clepper escribió:

...

OpenGL absolutely allows for platform specific behavior,

Wow, really sad

but it doesn't mean that one has to make an application behave differently on different plaforms.

sometimes there are reasons: e.g. performance (that's the reason why it is like it is)

on OSX we have upside-down textures by default for performance reasons; we also use rectangle textures for performance reasons (and because they are guaranteed to work on osx); on other platforms (w32, linux) rectangle textures might be not faster than normalized texs (or even slower) AND depending on the hardware or drivers installed, rectangle textures might not even be supported at all.

there are some good news, however: - in future releases all pixes will have top-down orientation (because there are virtually no codecs that provide bottom-up video material, and for images the performance penalty is not so big (and is blananced by the performance gain for videos) - the user will be able to set the default texture type on their systems in a central place (so they can guarantee themselves that they always have rectangle textures (if supported, that is) - eventually we will find a way to use texture matrices to unify texcoords for shaders and complex geometries (therefore: always premultiply your texcoords with the current texture matrix in your shader - even if it doesn't do anything right now)

fgmasdr IOhannes