I'm sending a bitmap as a uniform to a fragment shader with THREE.ImageUtils.loadTexture(). What's the simplest way for the fragment shader to access the size of the image in pixels?
Pass the values you want to the shader as uniforms.
Related
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 want to implement MRT in opengl es 3.0. Thus has created a framebuffer with texture as a GL_COLOR_ATTACHMENT0 attachment of type GL_RGBA32UI. Rendering a textured image of GL_RGBA32UI on that framebuffer. Then reading the framebuffer data as a texture and applying it as a texture in default buffer. (Basically render to texture using INTEGER texture)
I am trying to use same fragment shader for both my customize FBO and default one.
precision highp float;
uniform highp usampler3D stexture;
in vec4 out_TexCoord;
uniform highp uint range;
layout(location = 0) out uvec4 uex_colour;
layout(location = 1) out vec4 ex_colour;
void main(void)
{
uex_colour = uvec4(texture(stexture, out_TexCoord.xyz));
ex_colour = vec4(texture(stexture, out_TexCoord.xyz))/(range);
ex_colour = vec4(vec3(ex_colour.xyz), 1.0);
}
Want to use uex_color for rendering into the customize framebuffer and ex_color to render in default framebuffer.
Tried using glDrawBuffer(1, {GL_COLOR_ATTACHMENT0 }) for my FBO, but not able get how to use ex_colour for default framebuffer.
I think you would save yourself a lot of headache by using two different shaders. The allowed sets of values for glDrawBuffers are much more restrictive in ES 3.0 than in full OpenGL.
Specifically in your case, with the fragment shader you're trying to use, what you want in the back buffer is output 1. But for the default framebuffer, you can have only one draw buffer, which has to be GL_BACK. So you can only use output 0 for drawing the back buffer.
It actually looks like you might be trying to render to the texture and use the texture in the same rendering pass. If that's the case, it's a really bad idea. It sets up what the specs call a "rendering feedback loop". You can read up on the details, but it's generally not going to work. And you couldn't render to an FBO and the default framebuffer at the same time anyway.
You need to do one pass that renders to the FBO to generate your texture, then another pass to render to the default framebuffer, sampling the texture. You will use different shaders for these two passes.
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 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.
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.