17
votes
Accepted
Performance of Compute Shaders vs. Fragment Shaders for Deferred Rendering
After more analysis, the TL;DR here is that, yes, the slowdown is due to memory locality, and yes the pixel order is to blame. More interestingly, by writing the shader differently, we can greatly ...
- 1,950
9
votes
Using a LUT to speed up a trig heavy shader for mobile devices
It has been suggested in comments repeatedly, but noone felt the need to give a proper answer, so for the sake of completeness, a straight-forward and common solution to this problem might be to use a ...
- 1,674
7
votes
Accepted
Fragment shader's output variables
It works almost exactly the same way as vertex shader inputs.
In vertex shaders, you have inputs. And these inputs represent vertex attribute indices, the numbers you pass to ...
- 9,697
7
votes
Accepted
Why does substracting -1 in shader fail for a float data type?
Without seeing the error message I can't be sure but I think it's failing on the 1 being int instead of a float.
float inv_coord = v_coord - 1.0;
There is a ...
- 5,920
6
votes
Accepted
How to ensure a fragment shader only runs once
I don't think your approach is viable for a variety of reasons.
a GPU is heavily cache-dependent for performance. Pulling the same pixels over and over will just measure how fast a cache hit is. ...
- 5,920
5
votes
Accepted
Understanding fragment shader coordinate system
Everything in this code functions as intended, until I try to translate the entire grid (grid lines) to the center of the screen by adding v_Resolution.x / 2 to uv.x.
Not sure what your intention is ...
- 1,233
5
votes
Advice on how to create GLSL 2D soft smoke/cloud shader
There is good glsl source of noise (simplex noise) online to make real time noise. In addition to this, to make effect of moving fog/smoke like in this video you can make 3D FBM function. This is my ...
- 2,119
5
votes
Accepted
Advice on how to create GLSL 2D soft smoke/cloud shader
Noise functions are definitely your friend here—FBM would be one good candidate. You’re right that it can look too uniform on its own, but if you blend multiple layers of it together, using different ...
- 2,132
4
votes
Will the gaussian kernels in this fragment shader be computed for every fragment?
It depends. On a desktop, if the Gaussian function is always called with the same arguments, the shader compiler will probably optimize it so it's evaluated only ...
- 4,380
4
votes
Accepted
Ray tracing - partial derivatives for texture lookup
Yes, ray differentials are the way to go. The Paper by Igehy introduces them for the use case of filtered texture lookups. When generating the primary rays, you initialise the differentials to reflect ...
- 706
4
votes
Accepted
Z buffer working in OpenGL
When depth testing is enabled, the testing occurs after the fragment shader executes. The procedure is relatively simple (and spelled out pretty well here):
Get depth of fragment
Test against depth ...
- 1,353
4
votes
Accepted
Curve rotation in GLSL fragment shader
You are doing completely different things in Matlab than in your Fragment Shaders.
In Matlab you are generating bunch of points that can be drawn anywhere on the screen and then you are transforming ...
- 56
4
votes
Accepted
Help me understand the voronoi shader
1) Scale the texture coordinates from [0,1]x[0,1] -> [0,3]x[0,3]. It works with higher integer scales as well. This creates an imaginary 3x3 tiles grid.
st *= 3.;
...
- 438
4
votes
Accepted
SDF rendering for large world
You tile idea seems to be a good one to cut down on local complexity. You can't reasonably evaluate every primitive everywhere. Not if you want good performance anyway. So you need a simplified ...
- 1,585
3
votes
gl_FragCoord and glViewport
since that is the case for window-space coordinates in the vertex stage.
There are no "window-space coordinates in the vertex stage". Or at least, not in the vertex shader.
Window-space is ...
- 9,697
3
votes
Accepted
OpenGL ES Frag Shader - Branching
I think the most efficient way might be either
return float(shadowValue > shadowTexZ);
or
...
- 1,436
3
votes
Accepted
Count number of green fragments that are within a given distance from each screen fragment
You're getting a cross shape in the output because in your loop, you're counting pixels on the center row and column multiple times. For example the pixel at (0, 0) offset will be counted on every ...
- 24.8k
3
votes
Accepted
How to avoid declaring sampler outside of statement?
Background
In order to support mipmapping, the texture sampling system needs to know what scale the texture is being displayed at. In order to determine that scale automatically, the derivatives (or “...
- 991
2
votes
Accepted
How to correctly implement Lambertian BRDF with point light
It doesn’t matter that it’s a point light; the 1/π normalization factor is what’s causing your surface to be 1/π as bright as you’d like it to be. You can either up your light intensity so the maximum ...
- 2,132
2
votes
Accepted
Shader won't work
If you are using Processing the variable lightPosition must be declared as a vec4, otherwise it won't be passed in, and will be ...
- 238
2
votes
Will the gaussian kernels in this fragment shader be computed for every fragment?
The shader compiler will very likely perform common-subexpression consolidation, and compute that function once, and reuse it each time it appears in the shader.
You might think that, since ...
- 593
2
votes
Accepted
Alpha component in color buffer affects RGB components?
It looks like you're drawing with pre-multiplied alpha. This means that the red, green, and blue channels have been multiplied by the alpha channel. So your shader should look more like this:
...
- 3,401
2
votes
Interpolation in Graphics Pipeline
The rasterizer determines, which pixel is rendered depending on vertex positions that come out of the vertex shader. For each rasterized pixel, the rasterizer knows where it lies inside the triangle ...
- 1,233
2
votes
Is it possible to override or disable blending per pixel
You seem to be using additive blending against its purpose. Additive blending is supposed to represent light from multiple sources being combined. It is not physically possible for one source of light ...
- 9,697
2
votes
Anti-Aliasing simple circle fragment shader
Probably the simplest way is to use smoothstep to make a transition from white to black:
...
- 215
2
votes
Accepted
Are stencil buffer dimensions required to match render target dimensions?
When the framebuffer attachment sizes differ, rendering will only happen to the smallest size supported by all attachments (i.e. a rectangle of minimal width & height among all the attachments). ...
- 215
1
vote
Accepted
gl_ClipDistance vs gl_CullDistance
The two are different because they do different things. Clipping and culling aren't the same thing at all. If an edge crosses a clip plane, the primitive has to be clipped to be within that plane. ...
- 9,697
1
vote
Can I write histogram equalization, blurring, sharpening grayscale image etc.. as shader programs with openGL?
Yes you can. There are basically two approaches:
You draw everything to a framebuffer object. Then you apply image processing fragment shaders to resulting texture of the previous draw call, where ...
- 461
1
vote
What is the most efficient line algorithm using a shader program
Here is a (mostly) minimal version of an SDF for a line segment using a signed distance field as suggested in the comments. I take no credit for this code, it is your function pieced together with IQ'...
- 3,030
1
vote
Accepted
How to pass only the needed portion of the data calculated in a fragment shader to another fragment shader?
I'm assuming that you don't know how many objects there will be or have any way to index them until the image processing operations are completed, i.e. you have some final pass that determines for ...
- 24.8k
Only top scored, non community-wiki answers of a minimum length are eligible