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Questions tagged [opengl]

For questions involving use of the OpenGL graphics library.

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Applying perspective divide on x and y only?

In the derivation of perspective matrix, z-value is shifted to w-value so that when perspective divide is applied to the result of matrix-multiplication with position values, the value of z can be ...
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0answers
11 views

How to use boolean operations (eg. subtraction) on 3D triangulated objects, originally stored as a .obj file, using openGL or other libraries?

What I would like to do is to create a crater on a field. To do so, I thought that creating a universal crater object (something cone-shaped) and then subtracting it from the field on a specified ...
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19 views

GL_DEPTH_CLAMP has no effect (reverse z)

In an effort to improve cascaded shadow maps, I have looked into using GL_DEPTH_CLAMP and moving the near and far plane just around the actual view frustum instead of the global bounding box. But the ...
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1answer
48 views

Why is cos(𝜃) in the denominator in the reflectance equation and in the numerator in the shading equation?

Background: I'm reading https://learnopengl.com/PBR to learn about PBR. In the theory slide (https://learnopengl.com/PBR/Theory), the author has the reflectant equation as The theta (the angle ...
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1answer
45 views

Sphere Texture Mapping Algorithm

I am trying to generate UV coordinates automatically to map a texture on a sphere. The problem is with seams when going from 0.8 to 0.2 there is a discontinuity and interpolation in fragment shader ...
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1answer
32 views

Difficulty including GLM into Visual Studio with OpenGL

I have been trying to implement GLM (math library) into Visual Studio with OpenGL. I have followed and watched many online resources that point me to include only the GLM folder inside the ...
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0answers
58 views

Convey screenspace bounding box of rendering result

Imagine I render to an FBO some arbitrary geometry. Geometry can be rendered via single or multiple draw calls. For the sake of the question, assume I know nothing about geometry or transformation ...
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0answers
50 views

Show the edges between the clipping plane and clipped objects [closed]

I want to utilize shaders to not only discard fragments if they are on one side of a predefined plane but also render a contour along the intersection. My fragment shader currently does something ...
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1answer
72 views

This function syntax is confusing me

gladLoadGLLoader((GLADloadproc)glfwGetProcAddress) I have never seen this syntax before. Presumably glfGetProcAddres is a function, but it has the brackets behind it. Is this only possible in open gl ...
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1answer
59 views

GBuffer: Framebuffer with different texture format types?

I rely on this answer from Nathan Reed: How much precision do I need in my G-Buffer? It is proposed to use two different texture formats for one Gbuffer. However as far as I know, color texture ...
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1answer
59 views

OpenGL Unable to retrieve the values of data sent to shader using textures

I've been following these tutorials and i can't figure out how to send data to shaders using textures. https://en.wikibooks.org/wiki/OpenGL_Programming/Scientific_OpenGL_Tutorial_02 In this tutorial ...
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2answers
102 views

How do I use texture coordinates of a .obj file in OpenGL?

I have an obj file, with texture coordinates (indicated by vt). How would I use this to load textures in OpenGL?
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0answers
62 views

Specular/Diffuse light on an icosahedron opengl

I'm having a problem with my model here. I draw an icosahedron using GLUT, and the radius is set to 0.8. The info of the coordinates are listed below: (X and Z are calculated since our radius is 0.8) ...
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1answer
38 views

GL_SAMPLE_ALPHA_TO_COVERAGE and depth testing

I am currently looking into alternatives to my current, somewhat slow but exact, OIT approach. Specifically, GL_SAMPLE_ALPHA_TO_COVERAGE to convert the alpha value into a per-sample mask. ...
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1answer
57 views

Efficiently drawing multiple instances of 3D objects

I was able to write the following working code to draw any number of "sprites" (defined as 2 tringles, 6 vertices) ...
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1answer
67 views

Convert shader from GLsl 1.50 to 1.30

I'm a newbie with OpenGl and I'm stuck in following the tutorial. I found this tutorial with these shaders ...
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1answer
57 views

Why is glreadpixels only working in certain cases?

If I try to read the screen with glreadpixels and then draw the same thing again using gldrawpixels it works, BUT if and only if ...
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1answer
143 views

Is a single shader and 1x1 pixel white sampler more efficient than frequent switching between shaders with and without samplers?

I have some existing OpenGL code that I am porting to Vulkan. The question is somewhat relevant to both OpenGL and Vulkan. I am rendering some primitives using textures, some single channel, others ...
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1answer
140 views

Translate an arcball camera upwards or left-right

This problem is giving me a really hard time. I'm always looking at the origin and have a camera that moves around it in an arcball mode. That part works beautifully: I'm calculating the camera ...
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1answer
122 views

Project vertex onto plane

What I have: a plane given by its normal$\ n $ and a point on the plane$\ p $. a 3D-point$\ v $. a direction$\ d$. What I need: the projection of$\ v$ along$\ d$ onto the plane. How can I ...
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1answer
124 views

Drawing Directed Lines (with arrow endings)

I am working on a simple graph viewer with OpenGL. My problem with is directed edges. I tried to draw arrow endings with GL_TRIANGLES but somehow my calculations are off. I've used direction cosine ...
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1answer
82 views

Is it possible to access adjacent vertex data in tessellation evaluation shader?

I'm trying to render thick cubic Bezier curves using the whole OpenGL 4.5 pipeline: I render a patch with 4 control points. Vertex shader is simply pass-through to tessellation control shader. ...
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1answer
84 views

LoopBlinn Cubic Curve Rendering - Serpentine arteffect

I am trying to implement the Loop-Blinn cubic curve in java using the following source codes GPU-Curve-Rendering and WebCore. Both of them are showing few arteffects and i cannot figure out why. Here ...
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2answers
169 views

How can I draw this style of grid?

I'm trying to write code (in any language) to render this 3D grid, matching the look and colors as closely as possible:
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1answer
67 views

Adding vbos to a vao once it has been created

Is it possible to add vbos to vbos after their creation? For example (pseudo-code): ...
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1answer
88 views

Do operating programs such as Microsoft Office or Windows Explorer use OpenGL to draw?

I have a server and my only monitor is plugged into its graphics card. My question is - do all programs (Windows explorer, Excel whatever) draw their output using the graphics card and more ...
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1answer
75 views

How to include OpenGL extension loader in my project

I have a modern OpenGL project hosted publicly. I want to create the easiest experience so someone can just clone the repo and have it just work. So far, I have included (as git submodules) the ...
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0answers
52 views

Identification of visible area of a plane in OpenGL

I have somewhat generalized version of this question: https://stackoverflow.com/questions/52475104/how-to-show-visible-part-of-planar-world-rendered-with-3d-perspective-on-topside -‎ I would also like ...
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2answers
225 views

What's the point of “work groups” for OpenGL compute shaders?

glDispatchCompute has the number of work groups as arguments. What is the point of having work groups? How are they useful, compared to just having NxM independent pixel calculations with a known (x,...
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1answer
95 views

How to apply wire texture for realistic rendering of embroidery?

I am building an algorithm which takes a bitmap image as input and render the image as an embroidery design. The different steps are : Vectorize the image, I keep only 5 colors (Done) Generate ...
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2answers
105 views

Relatively new to OpenGL, need guidance/tips on an assignment with interactive user input

I'm currently taking a Computer Graphics class at university, and have been given an assignment which involves loading an obj file and manipulating it with keyboard and mouse controls (eg. arrow keys ...
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1answer
181 views

Why are depth buffer values clamped to (0, 1)?

This is a simple question. I know that in OpenGL or other graphics API, the values stored in the depth buffer are automatically clamped to (0,1). I just want to know why people do this instead of ...
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1answer
47 views

What does “region to be shaded” mean in the PCF paper?

I am reading the percentage closer filtering (PCF) paper by Reeves, W. et al. (https://graphics.pixar.com/library/ShadowMaps/paper.pdf). At at section 3.2, it mentioned that "each shading calculation ...
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2answers
80 views

Can gl_WorkGroupSize be set outside the compute shader?

I am migrating code from CUDA to OpenGL compute shaders. I could not find a way to set the local workgroup size outside the shader; is there a way to set gl_WorkGroupSize in the calling program like ...
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1answer
130 views

Multiple VAO share a EBO (OpenGL 3.3)

As mentioned here, multiple VAOs can share a single VBO. However, can multiple VAOs share a single EBO? For example, I want to create 2 rectangles. So, I do the following: ...
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1answer
85 views

Difference between relativeOffset and offset in VAO with Direct Access Ext

Using The DSA Ext with opengl , API calls to guide opengl to the buffer format are : ...
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1answer
86 views

Issue with loading a texture on the GPU with OpenGL 4.1 Core profile

I’ve been trying to render a texture on the whole screen in OpenGL 4.1 using the Core profile and followed a few tutorials on the matter, but all I have so far is a blank screen. I tried using my ...
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0answers
61 views

glTexSubImage3D throws GL_INVALID_ENUMERATION on NVIDIA

I'm having problems when using the following statement on different GPUs: glTexSubImage3D(target, 0, 0, 0, 0, width, height, layers, format, type, NULL); on ...
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0answers
63 views

How to compute size of OpenGL's image buffer?

I am trying to retrieve OpenGL's color buffer with the following code. My program is crasing in the line that makes the call to glReadPixels() apparently image.data ...
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0answers
335 views

How Skia uses OpenGL backend?

Skia 2D's one notable backend in OpenGL, but how does it work under the hood to render? Say, we need to draw an anti-aliased circle. Does Skia: make a quad (using 2 triangles) and paint the circle ...
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1answer
65 views

Drawing a plane super-imposing over another plane

I wish to draw a plane (A building's floor in this case) over a canvas plane (assume the plane is smooth). The planes are drawn as QUADS. The problem is that both plane are located at the same height....
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0answers
80 views

Hard edges appearing in voxel cone tracing (how to remove them?)

I am generating shadows using a voxel pyramid (commonly called voxel cone, although I hate that term). Some of my shadows come as expected, however some are very strange. For example in this image: ...
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0answers
39 views

Problem with imageStore to 3D texture on old AMD card

I've been updating an old project that does Marching Cubes using compute shaders, and it fails on my laptop with an old AMD GPU (7670M). After investigating a bit, I found the problem is with writing ...
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0answers
102 views

Changing coordinate system from texelFetch to textureLod is breaking the algebra

I have a scene rendered using texelFetch() and I am trying to modify the shader to use textureLod() instead. This is the image generated with texelFetch: When I try to change the shader to use ...
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0answers
229 views

OpenGL - Fit High/Low Resolution Image/Texture to a particular size Window

Consider a ray tracer written in OpenGL and using GLFW as a window toolkit. There are basically 2 options to display the ray-traced image. 1) Create a RenderBuffer ...
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0answers
72 views

Voxel cone tracing artifacts (what causes them and how to solve them)?

I am trying to generate soft shadows using voxel cone tracing. Which gives me the next images: In the first image you can see an artifact of a sequence of horizontal shadows alternating with ...
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0answers
158 views

How exactly do soft shadows get generated using a voxel cone tracing rendering technique?

Let's assume we have voxelized a scene, and all of our materials have an opacity level of 1. The reuslt would then look like: If we raytraced the final volume that gets generated after rasterization. ...
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2answers
230 views

How to convert from glBegin() and glEnd() to VBOs?

How to convert from glBegin() and glEnd() to VBOs (Vertex Buffer Objects)? I found a simple example here: ...
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2answers
126 views

What is OpenGL's paradigm?

OpenGL is not object-oriented, but more like "switches you turn on"? Like ...
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1answer
161 views

Self intersection artifacts in 3D image raytracing

I am developping a voxel raytracer for global illumination. I have been successful in multiple aspects but there is a problem I am not sure how to solve. The model works as most other Voxelization ...