Questions tagged [opengl]
OpenGL (Open Graphics Library) is a graphics standard and API which is platform-independent and available for desktop, workstation and mobile devices. It is designed to provide hardware-accelerated rendering, and hence gives greatly improved performance over traditional software rendering. OpenGL is used for applications like CAD software and computer games. The OpenGL standard, as well as OpenGL ES, is controlled by the Khronos group.
722
questions
71
votes
6
answers
50k
views
How can I debug GLSL shaders?
When writing non-trivial shaders (just as when writing any other piece of non-trivial code), people make mistakes.[citation needed] However, I can't just debug it like any other code - you can't just ...
- 2,720
65
votes
10
answers
46k
views
Should new graphics programmers be learning Vulkan instead of OpenGL? [closed]
From the wiki: "the Vulkan API was initially referred to as the 'next generation OpenGL initiative' by Khrono", and that it is "a grounds-up redesign effort to unify OpenGL and OpenGL ES into one ...
- 885
27
votes
2
answers
39k
views
GLSL. Can someone explain why gl_FragCoord.xy / screenSize is performed and for what reason?
I'm new to shaders and know that you can color pixels with gl_FragColor but sometimes there is this thing:
...
- 373
26
votes
2
answers
18k
views
What is fwidth and how does it work?
The OpenGL documentation states that fwidth returns the sum of the absolute value of derivatives in x and y.
What does this mean in less mathematical terms, and is ...
- 577
26
votes
1
answer
10k
views
What does "st" mean in the context of OpenGL?
I've seen the term st come up a few times when looking at other OpenGL fragment shaders. However, I don't know what it stands for or what it's used for. Here's an ...
- 363
18
votes
3
answers
6k
views
How can I debug what is being rendered to a Frame Buffer Object in OpenGL?
I have a point cloud that is being rendered to the screen. Each point has its position and color as well as an ID.
I was asked to render the IDs for each point to a texture so I created a FBO and ...
- 969
18
votes
1
answer
7k
views
What does "makeContextCurrent" do exactly?
I am pretty confused about that function. GLFW Context reference says as follow:
This function makes the OpenGL or OpenGL ES context of the specified
window current on the calling thread. A ...
- 657
18
votes
2
answers
18k
views
GL_STATIC_DRAW vs GL_DYNAMIC_DRAW vs GL_STREAM_DRAW: does it matter?
In OpenGL the buffer object functions (glBufferData, glBufferSubData, and probably a few others) have a parameter ...
- 4,380
18
votes
1
answer
2k
views
Is there any way to generate primitives in a geometry shader without any input geometry?
A few years ago I tried to implement this GPU Gem in OpenGL to generate 3D procedural terrain using Marching Cubes. The article suggests to implement Marching Cubes in a geometry shader to maximum ...
- 2,720
17
votes
2
answers
11k
views
Cause of shadow acne
I know how shadow mapping works but I am not getting the cause of shadow acne!
Can anyone tell me cause of shadow acne in a simple way and how is it related to depth map resolution?
16
votes
3
answers
6k
views
What are some methods to render transparency in OpenGL
Alpha blending can be turned on to make surfaces transparent, like so:
...
- 669
16
votes
2
answers
13k
views
How to implement a trackball in OpenGL?
After so much reading about transformations it is time to implement a trackball for my app.
I understand I have to create a vector from the origin to where the mouse is clicked and then another from ...
- 969
15
votes
1
answer
3k
views
Synchronizing successive OpenGL Compute Shader invocations
I have a couple of compute shaders that need to be executed in a certain order and whose outputs depend on previous inputs. Ideally, I'll never need to copy a buffer client-side and do all of my work ...
- 1,144
15
votes
1
answer
3k
views
OpenGL compatibility, naming conventions and ARB vs EXT
I thought I had formed a general understanding of how OpenGL naming conventions and extensions worked, until I stumbled upon a case that confused me.
Here's my understanding so far:
No suffix -- e.g....
- 577
14
votes
1
answer
2k
views
When to disable perspective correct interpolation ( noperspective )
In GLSL, perspective correct interpolation of vertex attributes is the default setting - one can disable it for specific vertex attributes by using the noperspective qualifier. Other than in post-...
- 243
13
votes
1
answer
4k
views
Do I need to rebind uniforms or attributes when changing shader programs?
Rendering the scene usually involves more than one shader program which, in my case, all use the same attributes and share at least some of the uniforms. To have them working properly, I currently ...
- 1,310
13
votes
1
answer
19k
views
OpenGL GLSL - Sobel Edge Detection Filter
With respect to this topic I've successfully implemented the Sobel Edge Detection filter in GLSL. Here is the fragment shader code of the filter:
...
- 601
13
votes
2
answers
3k
views
Derivative maps vs. Tangent Space Normal maps
I discovered that some engines use derivative maps instead of tangent space normal maps.
After some reading, it seems to be a really awesome way to replace tangent space normals but are there some ...
- 1,219
13
votes
1
answer
6k
views
Loop performance in a shader
I am wondering what's the best way to integrate a dynamic loop function in a shader?
First, it seems that dynamic arrays are not possible. So, is it better to create a maximum size array and only ...
- 1,219
12
votes
3
answers
15k
views
Dynamic Array in GLSL
Is it possible to have a dynamic array in a GLSL shader? For instance, what if I have something like this in my GLSL Shader:
...
- 451
12
votes
2
answers
10k
views
OpenGL - Detection of edges
I'd like to load arbitrary meshes and draw thick black lines along the edges to get a toon-shading like look.
I managed to draw a black silhouette around the objects by using the stencil buffer. You ...
- 601
12
votes
4
answers
2k
views
Does it matter whether I learn OpenGL or Direct3D?
Are the differences between these two APIs minor implementation details that mean once I have learned one I can use it for everything? Or are there reasons for learning one rather than the other if I ...
12
votes
2
answers
839
views
Is it possible to find out how many fragments made it through the stencil test?
I have an OpenGL application which uses stencil tests quite extensively to render irregular shapes (a bit like a simple 2-D CSG). If I could find out how many fragments passed the stencil test and ...
- 2,720
12
votes
1
answer
763
views
Is modifying a texture (painting on it) considered a "state change"?
The convention in graphics is that performing fewer state changes is better than performing more state changes (switching shaders, binding buffers, binding textures, etc.). For textures, it is faster ...
- 227
12
votes
2
answers
39k
views
Is there any reason to prefer Direct3D over OpenGL?
So I was reading this, I sort of got the reason why there are a lot more games on Microsoft windows than on any other OS. The main issue presented was that Direct3D is preferred over OpenGL.
What I ...
user3437
11
votes
4
answers
13k
views
Multiple viewports with modern OpenGL?
I use SDL2.
Currently my only shader has a MVP matrix, and transforms the points with it.
I calculate my View and Projection matrix for a camera with GLM:
...
- 313
11
votes
1
answer
1k
views
Why do adjacent triangles never overlap when rasterized?
Apologies for the following noob question, it's just I can't find a satisfactory answer anywhere...
When I render a simple axis-aligned quad made up of two triangles, I don't understand why there's ...
- 213
11
votes
1
answer
324
views
Do the alignement and declaration order of uniforms matter?
In the section 6.4 Constant Buffers of the book Practical Rendering & Computation with Direct3D 11 (pages 325, 326) it is mentioned:
By default, the HLSL compiler will attempt to align ...
- 4,380
10
votes
3
answers
5k
views
How to do texturing with OpenGL direct state access?
How do you use textures with direct state access in OpenGL?
I have the following in my code, which seems to work:
...
- 183
10
votes
1
answer
2k
views
What is the modern equivalent of display lists?
Display lists were an OpenGL feature that could, in theory, accelerate any part of the API by storing a group of commands for later use. In my understanding, this makes a lot of sense with regards to ...
- 4,380
10
votes
1
answer
2k
views
Is it good practice to use all the available texture units?
When applying multiple textures to a mesh, like for bump-mapping, I usually bind the textures to the first few fixed texture units, e.g.: diffuse = unit 0, bump = unit 1, specular = unit 2, then keep ...
- 1,439
10
votes
1
answer
3k
views
Screen capture of game video
I'd like to "hook" into a running game, say Mario Bros, and capture each frame rendered... saving that frame to an image file. A good example of something similar is FRAPS. --Note: I don't want to ...
- 269
10
votes
1
answer
524
views
What are sample gaps during scan conversion?
In this tutorial,
It is very often the case that triangles are rendered that share
edges. OpenGL offers a guarantee that, so long as the shared edge
vertex positions are identical, there will be no ...
- 237
10
votes
1
answer
594
views
Creating shared vertex normals on GPU
I've mostly succeeded at porting an implementation of Marching Cubes from CPU over to OpenGL compute shaders, but I haven't tackled normals yet and wondering the best way to go about it.
My ...
- 2,342
10
votes
1
answer
2k
views
Optimal memory access when using lookup tables on GPU?
I'm exploring isosurface algorithms on GPU for a bachelor's project (specifically concentrating on just binary in/out voxel data rather than real-valued fields). So I have a CPU implementation of good ...
- 2,342
10
votes
1
answer
2k
views
Is it possible to alpha blend multiple render targets using a specified alpha?
Say I have render targets 0 through N and RT 0 happens to have in its fourth component an alpha channel specified by a material or mask or something.
Is it possible to have the hardware compositor ...
- 267
10
votes
1
answer
232
views
Per Vertex Computation in OpenGL Tesselation
I try to implement a position based cloth simulation using hardware tesselation.
This means I want to just upload a control quad to the graphics card and then use tesselation and geometry shading to ...
- 1,800
9
votes
1
answer
15k
views
How to use GLSL texelFetch?
I have read the OpenGl documentation of texelFetch, which is:
gvec4 texelFetch(gsampler2D sampler, ivec2 P, int lod).
I know the first argument "sampler" is just a texture. But I am very confused ...
- 455
9
votes
2
answers
282
views
When is it better to upload partial model matrices to the vertex shader?
As of now, when rendering my scene and while iterating through the scene graph, for each node its model matrix is calculated from the parent's model matrix and the scene node's pose. This is quite ...
- 1,310
9
votes
1
answer
2k
views
Shadow Mapping artefacts
I've been playing around with shadow mapping in OpenGL using depth textures. The depth texture is fine and I can map it onto the scene but I have some strange artefacts on the back of the object:
My ...
- 193
9
votes
1
answer
3k
views
OpenGL specular shading - Gradient banding issues
I use Phong shading as my lighting model. Nevertheless, the specular shading produces gradients in the light cone:
Hopefully you can see the gradient starting from the lower left corner expanding ...
- 601
9
votes
1
answer
722
views
9
votes
1
answer
2k
views
Are draw calls executed in parallel or sequentially or both?
This a follow up for a question I answered on GameDev SE. The question was simply Is glDrawArraysInstanced in OpenGL parallel when drawing those instances?
My answer was in the lines of "the GPU ...
- 243
9
votes
2
answers
9k
views
Why do I need to inverse the orientation matrix of a camera to be able to translate it in the direction it is facing?
I've been going over some OpenGL learning resources and one of them is this article: Modern OpenGL 04 - Cameras, Vectors & Input in which the author presents an approach to building a ...
- 193
9
votes
1
answer
538
views
Rendering fog underneath water
I'm aware of glFog, which blends between the fog and surface colour based on distance to the camera, like this:
The equations are even given in the docs.
But the fog is applied immediately in front ...
- 669
9
votes
1
answer
2k
views
Writing to a compressed texture using a compute shader, with no extra copies
I'm trying to figure out what the best way is to generate an OpenGL texture using a compute shader. So far, I've read that pixel buffer objects are good for non-blocking CPU -> GPU transfers, and that ...
- 1,144
9
votes
2
answers
832
views
How to unproject quadrilateral into rectangle?
tl;dr: Math problem in projective geometry: How does one find some 4x4 camera matrix that gives a projection as illustrated below, such that points A,B,C,D are somewhere on the edges of the unit box (...
- 191
8
votes
2
answers
1k
views
Help me grasp Anisotropic Filtering (AF)
Lately I've been reading about texture filtering, namely Nearest-neighbor filtering, Bilinear filtering, Trilinear filtering, Anisotropic filtering, MIP maps, RIP Maps and so on.
From a high-level ...
8
votes
2
answers
752
views
Real-time translucency effect
While rendering my scene with OpenGL, I sometimes add an overlay which contains information, settings and a few draggable items. Currently, the overlay has a slightly transparent background to make ...
- 1,310
8
votes
1
answer
1k
views
How much precision (half, float, double, etc) is enough for a Color class?
While doing some reading on how real-time applications handle color under OpneGL, I noticed that some examples implemented Color as a collection of 4 floats, while ...
- 165