[PD] gem/GLSL: how to compute correct coordinates for rectangular textures

[Matteo Sisti Sette]

Jack escribió:

 > What about [pix_resize] after [pix_image] ?

Well I don't want to actually resize any image (i.e. actually modify 
pixel data).

But maybe you mean one [pìx_resize] after the [pix_image] of the left 
(not the ones on the right), "resizing" it with the size of the images 
on the right, those actually used as textures, so the image on the left 
would serve as a "dummy" image just to have the shader get the correct 
coordinates.

That may do the trick, however I will always need a "dummy" image. Is 
there a way to just _set_ the image size without having any image?

thanks
m.

Jack escribió:
> Le dimanche 03 janvier 2010 à 21:17 +0100, Matteo Sisti Sette a écrit :
>> Hi,
>>
>> I guess if I had a deep understanding of openGL I could find the answer, 
>> but I am obviously looking for a shortcut (at the moment) to solve the 
>> specific problem I'm facing which should be pretty simple.
>>
>> In the attached patch I try to use a trivial shader to texture a 
>> rectangle with an image; the uniform variable "curtex" tells the shader 
>> which texture to use.
>>
>> It works fine if all images have the same size; however, if the textures 
>> have different sizes, no matter the value of "curtex", the texture 
>> coords that are computed are correct for the image loaded by the 
>> [pix_image] that immediately follows the [glsl_program], but are not 
>> correct for other images.
>>
>> So the question is: how should I change the vertex and/or fragment 
>> shader code (or the patch maybe) so that the texture coordinates are 
>> computed according to the dimensions of the texture that is actually 
>> sampled?
>>
>> It is important to NOT assume that the textures come from [pix_image] 
>> objects, or at least, that they are loaded from image files: actually, 
>> in real life, textures may be the video input generated by a [pix_film] 
>> or an image captured by a [pix_snap].
> What about [pix_resize] after [pix_image] ?
> ++
> 
> Jack
> 
> 
>>
>> Thanks a lot in advance
>>
>> pièce jointe document texte brut (trivialshader.frag)
>> // porcodio
>>
>> #extension GL_ARB_texture_rectangle : enable
>> uniform sampler2DRect curtex;
>>
>> void main (void)
>> {
>>  vec2 xy=gl_TexCoord[0].st;
>>
>>  vec4 frontcolor = texture2DRect(curtex, xy);
>>  
>>  gl_FragColor = frontcolor;
>>  
>> }
>> pièce jointe document texte brut (test_trivial_shader.pd)
>> #N canvas 443 93 925 656 12;
>> #X obj 441 576 gemwin;
>> #X msg 437 515 create \, 1;
>> #X msg 484 547 destroy;
>> #X obj 58 177 glsl_vertex;
>> #X obj 59 313 glsl_fragment;
>> #X obj 143 211 change;
>> #X obj 160 342 change;
>> #X obj 155 385 t b f;
>> #X obj 153 418 pack 0 0;
>> #X obj 60 490 glsl_program;
>> #X msg 154 454 link \$1 \$2;
>> #X obj 60 567 pix_texture;
>> #X obj 188 24 bng 15 250 50 0 empty empty empty 17 7 0 10 -262144 -1
>> -1;
>> #X obj 69 33 gemhead 50;
>> #X obj 508 77 gemhead 23;
>> #X obj 511 259 pix_texture;
>> #X msg 519 221 texunit 1;
>> #X obj 664 260 pix_texture;
>> #X obj 661 78 gemhead 24;
>> #X floatatom 212 525 5 0 0 0 - - -;
>> #X obj 70 60 t a a;
>> #X msg 349 409 rectangle 1;
>> #X obj 348 384 loadbang;
>> #X msg 757 119 rectangle 1;
>> #X obj 762 53 loadbang;
>> #X msg 136 99 open trivialshader.vert;
>> #X msg 114 259 open trivialshader.frag;
>> #X obj 60 600 square 4;
>> #X obj 46 528 pix_image img1_.jpg;
>> #X obj 506 163 pix_image img2_.jpg;
>> #X obj 659 164 pix_image img3_.jpg;
>> #X msg 278 474 texunit 2;
>> #X msg 672 222 texunit 0;
>> #X floatatom 253 333 5 0 0 0 - - -;
>> #X msg 229 387 curtex \$1;
>> #X connect 1 0 0 0;
>> #X connect 2 0 0 0;
>> #X connect 3 0 4 0;
>> #X connect 3 1 5 0;
>> #X connect 4 0 9 0;
>> #X connect 4 1 6 0;
>> #X connect 5 0 8 0;
>> #X connect 6 0 7 0;
>> #X connect 7 0 8 0;
>> #X connect 7 1 8 1;
>> #X connect 8 0 10 0;
>> #X connect 9 0 28 0;
>> #X connect 9 1 19 0;
>> #X connect 10 0 9 0;
>> #X connect 11 0 27 0;
>> #X connect 12 0 25 0;
>> #X connect 12 0 26 0;
>> #X connect 13 0 20 0;
>> #X connect 14 0 29 0;
>> #X connect 16 0 15 0;
>> #X connect 18 0 30 0;
>> #X connect 20 0 3 0;
>> #X connect 21 0 11 0;
>> #X connect 22 0 21 0;
>> #X connect 22 0 31 0;
>> #X connect 23 0 17 0;
>> #X connect 23 0 15 0;
>> #X connect 24 0 23 0;
>> #X connect 24 0 32 0;
>> #X connect 24 0 16 0;
>> #X connect 25 0 3 0;
>> #X connect 26 0 4 0;
>> #X connect 28 0 11 0;
>> #X connect 29 0 15 0;
>> #X connect 30 0 17 0;
>> #X connect 31 0 11 0;
>> #X connect 32 0 17 0;
>> #X connect 33 0 34 0;
>> #X connect 34 0 9 0;
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> 
> 
> 


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