I am writing a Fragment shader for an Open GL ES application, and Im trying to clarify the difference between a Pixel and a Varying?
A varying type in OpenGL ES contains an optional, user-defined output from the vertex shader to the fragment shader (e.g. a surface normal if using per-pixel lighting). It is used to calculate the final fragment color (gl_FragColor) within the fragment shader. While a final color can be output from the vertex shader (e.g. if using per-vertex lighting) as a varying type, this is not the norm and depends on your desired shader behaviour.
A pixel is simply the smallest measured unit of an image or screen. The OpenGL ES pipeline produces fragments (raw data) which are then converted (or not) to pixels, depending on their visibility, depth, stencil, colour, etc.
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I am looking to color a fractal within my fragment shader in an WebGL project.
Within my fragment shader, I have a vec3 called Color that contains the RGB values from 0.0-1.0.
To make a fractal design similar to
but in black and white,
what would I need to set the Color vector to? This color is then multiplied by the Weighted Lighting for the gl_FragColor.
Mandelbrot shaders typically have loop that evaluates an escape condition. To make a monochrome image, simply set Color to vec3(0) if the number of iterations to escape is less than some threshold T, and set it to vec3(1) otherwise. For an example, see this shader toy.
I want to use a fragment shader to write back into a 3D-Sampler: There is an array of images as input (as uniform sampler3D) to my opengl-es-application and i want to perform some per-pixel operations on it. Can i use a fragment shader to calculate values for a 3D-Texture?
I happened to see this shader on shader toy.
https://www.shadertoy.com/view/ldf3W8
I wanted to know what:
uniform samplerXX iChannel0..3;
is?
I tried to look at the vertex shader, but I don't find any thing there.
Also how can I convert audio waves to a texture? (which is being done here)
I wanted to know what uniform samplerXX iChannel0..3; is?
uniforms are externally set variables that have the same value for invocations of the shader during a primitive draw (a vertex shader gets called for each vertex a primitive consists of, fragment shaders for each fragment (which is roughly translates to pixels) drawn to by the primitive).
samplers are OpenGL's way of binding texture units to a shader. In the actual OpenGL program you're loading the texture using glGenTextures, glActiveTexture, glBindTexture, glTexImage (and a bunch of other functions, but those are the important ones) and bind the texture unit selected with glActiveTexture to a sampler uniform.
Also how can I convert audio waves to a texture?
Textures are just interpolated lookup tables. You can place any data you like in a LUT. Most of the time a texture is used for image data, but you can loac PCM samples into it just as well. So you simply fetch PCM data from the audio API and pass it into a texture as data.
I'm trying to implement a simple linear gradient like in photoshop. The color interpolation between vertices seems to go by (additive?)numerical value rather than what you would expect in "paint blending." Here is a visual example with green and red:
The one on the left is roughly what I get, and I want to achieve the one on the right.
Is there any easy way to achieve this?
As #Andon commented, using the texture system is a good way to do this. Here's what you need:
Assign one (or more, but you only need one for this trick) texture coordinate(s) to each vertex when you set up attributes in your vertex buffer.
In your vertex shader, read that attribute and write it to a varying so it gets interpolated for use in the fragment shader.
In your fragment shader, read the varying -- this tells you how far along the gradient ramp you should be in the current fragment; i.e. a blending factor.
At this point, you have two choices:
Use a 1d texture image that looks like the gradient you want, and lookup into it with the texture2D shader function and the varying texture coordinate you got. This will fetch the corresponding texel color so you can output it to gl_FragColor.
Calculate the color blend in the fragment shader. If you pass in the endpoint colors in your shader as uniforms, you combine them according to the blending factor using whatever math you can do in GLSL (including things like Photoshop blend modes).
I'm trying to draw to a subrect of a texture based FBO, but am having difficulty. The FBO has dimensions of say 500x500 and I am trying to have the fragment shader only redraw say a 20x20 pixel subrect. Modiyfing the full texture works without difficulty.
At first I tried setting glViewport to the needed subrect, but it doesn't look to be that simple. I'm suspecting that the Vertex attributes affecting gl_Position and the varying texture coordinates are involved, but I can't figure out how.
Turns out that I was trying to modify the texture coordinate attributes, but was more easily able to just modify the viewport using glViewport and gl_FlagCoord within the shader.