Re: [PD] gem pix shear

Good explanations Marius. Thanx to share this. ++

Jack

Le mardi 28 juillet 2009 à 16:18 -0300, marius schebella a écrit :

Py Fave wrote:

...

so nice . exactly a good starting point for me . simple and efficient. you made it specially for me ? :-)

i'm trying to learn some glsl and i am not really fluent in it for the moment. to say the less. but reading your code makes me willing to try things.

hi, yes, atm I am trying to port shaders to pd and help people get started with it (it's part of my work for pdcon09, there is more to come...).

here is a version that will make it more clear what is going on. it does exactly the same thing as the shader I posted before, but splits the steps and has more comments.

------ snip stripeshear.frag ------

// create diamond pattern // shear (x/y) will change the angle of the diamonds // offset (x/y) will move pattern left/right/up/down // resize (x/y) will resize the height/width

// sampler2D is the texture connected in Gem uniform sampler2D texture;

// the data type vec2 means a vector of 2 floats, // to set this value from Pd send a list, e.g. // "shear 1.5 -0.7" uniform vec2 shear; uniform vec2 offset; uniform vec2 resize;

// take the pixel from position x/y and apply a new location to it // in the last line "texture" means the particular pixel // and "texCoord" the position where it will be drawn // the rest is the transformation from the original position to the // diamond pattern void main(void) { // gl_TexCoord[0].x is the original x position. (a float value) // gl_TexCoord[0].y the y position. // to shear the image add an offset based on the x/y position // and the factor "shear". float x = gl_TexCoord[0].x+gl_TexCoord[0].y*shear.x; float y = gl_TexCoord[0].y+gl_TexCoord[0].x*shear.y;

// to shift the whole pattern right/left or up down // add an offset // to access the values of the vector you can use // shear.xy (both) or shear.x or shear.y // shear.s is the same as shear.x and the same as // shear.r (letters stand for typical vectors: stuv, xyz, rgba) x = x + offset.x; y = y + offset.y;

// finally multiply the position offset to change // the size of x and/or y x = x*resize.x; y = y*resize.y;

// this step is not really necessary, but shows // how to put 2 floats into a vec2 vec2 texCoord = vec2(x,y);

// finally output the result as // gl_FragColor, which is a built-in glsl function gl_FragColor = texture2D(texture, texCoord); }

-------- snip end

marius.

...

Thanks

py

2009/7/28 marius schebella <marius.schebella@gmail.com mailto:marius.schebella@gmail.com>

Py Fave wrote:

    Thanks for your help.

    i would like to output a pix with this transformation,with image
    wrapping around ,
    so shearXY is not very practical in my situation.

    i would prefer to avoid using pix_snap too.

    i need it to be quite fast, working on a live 25 fps
    720*576(cropped to square) video feed.

    any other otions?

    would a GLSL shader do it ?


look at the attached shader, maybe it does what you want?
marius.

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