a GPU based cropper?

David Beaudry

Hi all,
I'm looking for a more efficient means of cropping an image. the goal is to crop, but not resize....i.e. where the image is cropped is just black. I have a patch below which works fine for what I need, however this method adds about 40-50% to my CPU...cycles I would much rather push to the GPU. Are there any shaders that do something similar? Again, patch below which hopefully illustrates what I'm trying to do.

Max Patch

Copy patch and select New From Clipboard in Max.

Much thanks!
David

reno-

David,

Here is a patch with a shader I use to crop...
Maybe it will be usefull for you.

regards,

Max Patch

Copy patch and select New From Clipboard in Max.

PS : the 2 shaders belows need to be saved on your hard drive with the correct name (see below the patch)

shader file : need to be named m_crop.jxs

        define crop param
        define edge size
        zoom factor
        offset factor for zoom
        interpolation on/off

frament shader file : need to be named m_crop.fp.glsl

// texcoords
varying vec2 texcoord0;
varying vec2 texdim0;

// samplers
uniform sampler2DRect tex0;

// resample dimensions
uniform vec4 crop;
uniform vec4 edge;
uniform vec2 zoom ;
uniform vec2 offset ;
uniform float interp;

// entry point
void main()
{
    // ramene coord [0-1] sur [0-texdim]
    vec4 cm = crop*vec4(texdim0.xyxy);
    vec4 am = edge*vec4(texdim0.xyxy);

    // calcul coord pixel fct zoom et offset
    vec2 fragcoord ;
    fragcoord = texcoord0/zoom - offset*texdim0 ;

    // verifie que dans borne du crop
    bool bnd = all(bvec4(texcoord0.x>cm.x,texcoord0.xcm.y,texcoord0.y
    // recupere couleur pixel
    vec4 fragColor = texture2DRect(tex0,mix(floor(fragcoord),fragcoord,interp));
    float alpha = fragColor.a ;

    // alpha blending hors des bornes
    if (bnd) {
        float ax = 1.;
        float ay = 1. ;

// a = smoothstep (cm, am, texcoord0.xyxy) ;

        if (texcoord0.x
            ax = smoothstep (cm.x, cm.x+am.x, texcoord0.x) ;
        }else if (texcoord0.x>cm.z - am.z){
            ax = smoothstep (cm.z, cm.z-am.z, texcoord0.x) ;
        }
        if (texcoord0.y
            ay = smoothstep (cm.y, cm.y+am.y, texcoord0.y) ;
        }else if (texcoord0.y>cm.w - am.w){
            ay = smoothstep (cm.w, cm.w-am.w, texcoord0.y) ;
        }

        fragColor.a = clamp(ax*ay, 0., alpha) ;
    }
    else {
        fragColor.a = 0. ;
    }

gl_FragColor = fragColor ;

}

David Beaudry

This is perfect! Thanks so much for your help with this. I really do need to start learning how to use shaders!

Thanks again!
David

Linden

sorry for the question:
how exactly should i save the shader?
do i have to add an header?

karl krach

i have exactly the same problem/question: how do i get this shader to work?
even if i do add a
thanks for help!
k

Rob Ramirez

Max Patch

Copy patch and select New From Clipboard in Max.

here's one using gl.pix:

karl krach

thanks for the quick reply!
in the meantime i as well found td.resample.jxs which does the job nicely...

Pedro Santos

Hi, Rob Ramirez. Thanks for the jit.gl.pix example!
But, as I understand it, it's essentially a smart workaround, i.e, you're masking the unwanted area through an alpha channel instead or really cropping the texture. Imagine that following the cropping process there's a long chain of slab processing. The GPU would be processing a larger size texture than really needed, lowering the performance. Would it be possible to build a jit.gl.pix that really crops the image, i.e, outputs a texture with smaller dimensions?

Thanks!