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<body class="article">
<div id="header">
<h1>Processing Shader Examples</h1>
</div>
<div id="content">
<div class="sect1">
<h2 id="_introduction">Introduction</h2>
<div class="sectionbody">
<div class="paragraph"><p>Welcome to Processing Shader Examples! This is where I try to learn about shaders using Processing and the Processing GLGraphics library (<a href="http://glgraphics.sourceforge.net/">http://glgraphics.sourceforge.net/</a>) and record my experiments and the lessons I learn. The repo for this project is here: <a href="https://github.com/atduskgreg/Processing-Shader-Examples">https://github.com/atduskgreg/Processing-Shader-Examples</a> Each sub-directory of this repo includes a shader example written in Processing along with a description.asciidoc file with notes about that particular example. I’ve also included all of the description files in this README for convenience (though that doesn’t seem to actually work on the project homepage in GitHub; if you’re reading this there, head to <a href="http://atduskgreg.github.com/Processing-Shader-Examples">http://atduskgreg.github.com/Processing-Shader-Examples</a> to see the real version).</p></div>
<div class="paragraph"><p>Right now, I’m mainly working from Graphics Shaders: Theory and Practice by Mike Bailey and Steve Cunningham (<a href="http://www.amazon.com/Graphics-Shaders-Practice-Mike-Bailey/dp/1568813341">http://www.amazon.com/Graphics-Shaders-Practice-Mike-Bailey/dp/1568813341</a>). Andres Colubri, author of the GLGraphics library, was an enormous help in getting started especially a session he taught at ITP Camp 2011 on the topic of Image Processing with Shaders in Processing. I’ve included the notes from that session here as well. It acts as a kind of introduction to the rest of this material, so we begin with it.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_image_filters_and_3d_effects_with_glsl_by_andres_colubri">Image Filters and 3D Effects with GLSL by Andres Colubri</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_on_the_cpu">On the CPU</h3>
<div class="ulist"><ul>
<li>
<p>
define geometry
</p>
</li>
<li>
<p>
beginShape() etc
</p>
</li>
<li>
<p>
define vertices:
</p>
<div class="ulist"><ul>
<li>
<p>
vertex coords
</p>
</li>
<li>
<p>
colors
</p>
</li>
<li>
<p>
connectivity
</p>
</li>
<li>
<p>
normals
</p>
</li>
<li>
<p>
texturecoords
</p>
</li>
<li>
<p>
textures
</p>
</li>
</ul></div>
</li>
</ul></div>
</div>
<div class="sect2">
<h3 id="_on_the_gpu">On the GPU</h3>
<div class="ulist"><ul>
<li>
<p>
GOAL: convert geometry into pixels
</p>
</li>
<li>
<p>
Vertex Shader:
</p>
<div class="ulist"><ul>
<li>
<p>
convert coordinates to screen space
</p>
</li>
<li>
<p>
takes 3D geometry and outputs 2D geometry
</p>
</li>
</ul></div>
</li>
<li>
<p>
Fragment/Pixel shader:
</p>
<div class="ulist"><ul>
<li>
<p>
converts 2D geometry to an array of pixels: rasterization
</p>
</li>
<li>
<p>
blending algorithms
</p>
</li>
<li>
<p>
lighting is applied
</p>
</li>
<li>
<p>
leads to final pixel color
</p>
</li>
</ul></div>
</li>
<li>
<p>
GPU is highly parallel
</p>
<div class="ulist"><ul>
<li>
<p>
can draw every pixel simultaneously
</p>
</li>
<li>
<p>
GPU has many cores, hundreds
</p>
</li>
<li>
<p>
NVidia 5706TX has 512 cores
</p>
</li>
</ul></div>
</li>
</ul></div>
</div>
<div class="sect2">
<h3 id="_play_with_shaders_in_processing">Play with Shaders in Processing</h3>
<div class="ulist"><ul>
<li>
<p>
Andres' GLGraphics library: <a href="http://glgraphics.sourceforge.net">http://glgraphics.sourceforge.net</a>
</p>
<div class="ulist"><ul>
<li>
<p>
works with Processing 1.5x not 2.0
</p>
</li>
</ul></div>
</li>
<li>
<p>
GLGraphics > Examples > Textures > BasicUse, etc.
</p>
</li>
</ul></div>
</div>
<div class="sect2">
<h3 id="_use_shaders_for_2d_image_effects_post_processing">Use Shaders for 2D Image Effects/Post-processing</h3>
<div class="ulist"><ul>
<li>
<p>
Send an image to the GPU
</p>
<div class="ulist"><ul>
<li>
<p>
as a textured quad:
</p>
</li>
</ul></div>
</li>
</ul></div>
<div class="listingblock">
<div class="content">
<pre><tt>beginShape(QUAD);
texture(...);
vertex(...);
vertex(...);
vertex(...);
vertex(...);
endShape();</tt></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
draw the quad covering the whole screen
</p>
</li>
<li>
<p>
using orthographic projection
</p>
</li>
<li>
<p>
the vertex shader does nothing: "trivial"
</p>
</li>
<li>
<p>
the pixel shader is the interesting part
</p>
<div class="ulist"><ul>
<li>
<p>
does a texture lookup to get the color of each pixel
</p>
</li>
<li>
<p>
can apply transformations per pixel
</p>
</li>
<li>
<p>
custom transformation is written in GLSL
</p>
</li>
</ul></div>
</li>
<li>
<p>
result of shader operations gets copied into a new texture
</p>
<div class="ulist"><ul>
<li>
<p>
has to be a new texture or you get problems
</p>
</li>
<li>
<p>
use ping-pong technique of swapping back and forth between two textures on alternating frames
</p>
</li>
</ul></div>
</li>
</ul></div>
</div>
<div class="sect2">
<h3 id="_actually_writing_shaders">Actually Writing Shaders</h3>
<div class="ulist"><ul>
<li>
<p>
glsl file w/an XML filter file for GLGraphics
</p>
<div class="ulist"><ul>
<li>
<p>
filter file combines vertex/fragment shaders and declares parameters
</p>
</li>
</ul></div>
</li>
<li>
<p>
example of swapping red and green component of an image on the cpu:
</p>
</li>
</ul></div>
<div class="listingblock">
<div class="content">
<pre><tt>PImage img;
PImage dest;
void setup(){
size(1600,600, JAVA2D);
frameRate(180);
img = loadImage("landscape.jpg");
img.loadPixels();
dest = createImage(800, 600, RGB);
dest.loadPixels();
}
void draw(){
for(int i = 0; i < img.width * img.height; i++){
color c = img.pixels[i];
dest.pixels[i] = color(green(c), red(c), blue(c), alpha(c));
}
image(img, 0,0);
image(dest,800,0);
println(frameRate);
}</tt></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
Equivalent example on the GPU:
</p>
</li>
</ul></div>
<div class="listingblock">
<div class="content">
<pre><tt>import processing.opengl.*;
import codeanticode.glgraphics.*;
GLTexture texSource;
GLTexture texDestination;
GLTextureFilter colorSwap;
void setup(){
size(1600, 600, GLConstants.GLGRAPHICS);
frameRate(180);
texSource = new GLTexture(this, "landscape.jpg");
texDestination = new GLTexture(this, texSource.width, texSource.height);
colorSwap = new GLTextureFilter(this, "colorSwap.xml");
}
void draw(){
colorSwap.apply(texSource, texDestination);
// synonym:
// texSource.filter(colorSwap, texDestination);
image(texSource, 0,0);
image(texDestination, 800,0);
println(frameRate);
}</tt></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
With a filter file ("colorSwap.xml") that looks like this:
</p>
</li>
</ul></div>
<div class="listingblock">
<div class="content">
<pre><tt><filter name="colorSwap">
<description>Reverse red and green components of each pixel</description>
<fragment>colorSwap.glsl</fragment>
<textures input="1" output="1"></textures>
</filter></tt></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
and a fragment shader ("colorSwap.glsl") that looks like this:
</p>
</li>
</ul></div>
<div class="listingblock">
<div class="content">
<pre><tt>uniform sampler2D src_tex_unit0;
void main(void){
// get the location of the current pixel
// in the input texture
vec2 tex_coord = gl_TexCoord[0].st;
// read the color of the current pixel out of the
// input texture
vec4 src_color = texture2D(src_tex_unit0, tex_coord).rgba;
// output:
// set color of the fragment
gl_FragColor = vec4(src_color.g, src_color.r, src_color.b, src_color.a);
}</tt></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
GPU version runs 6 times faster at least
</p>
</li>
<li>
<p>
now, passing arguments into the shader
</p>
<div class="ulist"><ul>
<li>
<p>
in draw() add calls to setParameterValue()
</p>
</li>
</ul></div>
</li>
</ul></div>
<div class="listingblock">
<div class="content">
<pre><tt>void draw(){
// NEW LINES: pass arguments into the shader
colorSwap.setParameterValue("scaledMouseX", map(mouseX, 0, width, 0, 1));
colorSwap.setParameterValue("scaledMouseY", map(mouseY, 0, height, 0, 1));
colorSwap.apply(texSource, texDestination);
// synonym:
// texSource.filter(colorSwap, texDestination);
image(texSource, 0,0);
image(texDestination, 800,0);
println(frameRate);
}</tt></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
pass these parameters through in the xml:
</p>
</li>
</ul></div>
<div class="listingblock">
<div class="content">
<pre><tt><filter name="colorSwap">
<description>Reverse red and green components of each pixel</description>
<fragment>colorSwap.glsl</fragment>
<textures input="1" output="1"></textures>
<parameters>
<parameter type="float" name="scaledMouseX" label="">1</parameter>
<parameter type="float" name="scaledMouseY" label="">1</parameter>
</parameters>
</filter></tt></pre>
</div></div>
<div class="ulist"><ul>
<li>