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I am trying to texture a glutSolidTorus().
Here is my code:
glColor3f(1.0f, 1.0f, 1.0f);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, tiring);
glutSolidTorus(.55, 1.8, 25, 25);
glDisable(GL_TEXTURE_2D);
But it does not work. How can I texture glutSolidTorus()?
Except for glut*Teapot() none of the GLUT geometry primitives provide texture coordinates:
11 Geometric Object Rendering
GLUT includes a number of routines for generating easily recognizable 3D geometric objects. These routines reflect functionality available in the aux toolkit described in the OpenGL Programmer's Guide and are included in GLUT to allow the construction of simple GLUT programs that render recognizable objects. These routines can be implemented as pure OpenGL rendering routines. The routines do not generate display lists for the objects they create.
The routines generate normals appropriate for lighting but do not generate texture coordinates (except for the teapot).
You have several options:
Fixed-function texcoord generation
Shader-based texcoord generation
Reimplement glutSolidTorus() to add texture coordinates
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I have an image database on my computer, and I would like to load each of the images up and render them in 3D space, in OpenGL.
I'm thinking of instantiating a VBO for each image, as well as a VAO for each one of the VBO's.
What would be the most efficient way to do this?
Here's the best way:
Create just one quad out of 4 vertices.
Use a transformation matrix (not 3D transform; just transforming 2D position and size) to move the quad around the screen and resize it if you want.
This way you can use 1 vertex array (of the quad) and texture Coordinates array and 1 VAO and do the same vertex bindings for every drawcall however for each drawcall there is a different texture.
Note: the texture coordinates will also have to be transformed with the vertices.
I think the conversion between the vertex coordinate system (2D) and texture coordinate system is vertex vPos = texturePos / 2 + 0.5, therefore texturePos = (vPos - 0.5) * 2
OpenGL's textureCoords system goes from 0 - 1 (with the axes starting at the bottom left of the screen):
while the vertex (screen) coordinate system goes from -1 to 1 (with axes starting in the middle of the screen)
This way you can correctly transform textureCoords to your already transformed vertices.
OR
if you do not understand this method, your proposed method is alright but be careful not to have way too many textures or else you will rendering lots of VAOs!
This might be hard to understand, so feel free to ask questions below in the comments!
EDIT:
Also, noticing #Botje helpful comment below, I realised the textureCoords array is not needed. This is because if your textureCoords are calculated relative to the vertex positions through the method above, it can be directly performed in the vertex shader. Make sure to have the vertices transformed first though.
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I want the code in glslSandBox to a regular glsl. Suppose I have a quad mesh 3D displaced in a 3D scene. I want to create this "shadertoy-like" texture and apply to it. I'm aware about the transformations it requires : Screen - NDC - CLIPSPACE - WORLDSPACE, but still I'm struggling. http://glslsandbox.com/e#61091.0 this is an extremely simple shader, can you please demonstrate the normal vs and fs shader it would take to apply it to a 3D mesh in a 3D scene?
The shader you linked is a fragment shader drawing on a flat screen plane.
Typically, the corresponding vertex setup would be two triangles (potentially as a strip, meaning 4 vertices in total), covering the entire screen. In fact, you don't really have to be concerning yourself with any transformations, especially given that the fs uses gl_FragCoord and the resolution is being passed as a uniform.
VS:
#version 450
in vec4 position;
void main() {
gl_Position = position
}
Vertices (example, use with GL_TRIANGLE_STRIP):
-1, -1
-1, 1
1, -1
1, 1
After you cover the entire screen, you can now just switch this setup to render to texture; create a framebuffer, attach a texture to it, and render in the same way. Then you'll be able to use that texture on your 3D model. This will work well if the generated image rarely changes.
If you actually wanted to draw that in one pass, then you'll need to pass the texture coordinate as a varying variable, and use it instead of gl_FragCoord; no other changes should be necessary.
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My problem is that i want to take a kind of snapshot of a 3d scene manipulate that snapshot and draw it back to another viewport of the scene,
I just read the image using the glReadPixel method.
Now I want to draw back that image to a specified viewport but with the usage of modern OpenGL.
I read about FrameBufferObject (fbo) and PixelBufferObject (pbo) and the solution to write back the FrameBufferObject contents into a gl2DTexture and pass it to the FragementShader as simple texture.
Is this way correct or can anyone provide a simple example of how to render the image back to the scene using modern OpenGL and not the deprecated glDrawPixel method?
The overall process you want to do will look something like this
Create an FBO with a color and depth attachment. Bind it.
Render your scene
Copy the contents out of its color attachment to client memory to do the operations you want on it.*
Copy the image back into an OpenGL texture (may as well keep the same one).
Bind the default framebuffer (0)
Render a full screen quad using your image as a texture map. (Possibly using a different shader or switching shader functionality).
Possible questions you may have:
Do I have to render a full screen quad? Yup. You can't bypass the vertex shader. So somewhere just go make four vertices with texture coordinates in a VBO, yada yada.
My vertex shader deals with projecting things, how do I deal with that quad? You can create a subroutine that toggles how you deal with vertices in your vertex shader. One can be for regular 3D rendering (ie transforming from model space into world/view/screen space) and one can just be a pass through that sends along your vertices unmodified. You'll just want your vertices at the four corners of the square on (-1,-1) to (1,1). Send those along to your fragment shader and it'll do what you want. You can optionally just set all your matrices to identity if you don't feel like using subroutines.
*If you can find a way do your texture operations in a shader, I'd highly recommend it. GPUs are quite literally built for this.
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I have a flat surface drawn with a single fullscreen GL_QUAD.
I want to deform this surface at each point specified by my GL_Texture2D, preferably through some kind of shader.
In my mind, black could correspond to flat and white could correspond to a hill.
I want to have about 4 million points on my terrain and update them at each step in my program.
How would I use a geometry shader to do this? Is a shader able to generate new veritices?
The simplest way would be to generate a large triangle strip grid, upload it to a VBO and draw it, using the vertex shader to alter just the up coordinate. The vertex shader can also generate normals from the heightmap (or supply a normal map), which then get passed to the fragment shader for lighting.
To avoid storing a huge amount of data for the vertices, use glVertexID to generate the vertex positions from scratch in the vertex shader. Don't bind any buffers, simply call glDrawArrays(GL_TRIANGLE_STRIP, 0, lots).
As GuyRT mentioned, a tessellation shader would be good too and allow you to vary the tessellation detail based on the camera's distance to the mesh. This would be more work though.
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How can I add a glowing effect to a line that I draw? I'm using OpenGL for Linux.
You can implement the radial blur effect described on Nehe Lesson 36. The main idea is to render the drawing to a texture, and do that N times with a small offset after each render, until the drawing is ready to be copied to the framebuffer.
I've written a small demo that uses Qt and OpenGL. You can see the original drawing (without the blur) below:
The next image shows the drawing with the blur effect turned on:
I know it's not much, but it's a start.
I too once hoped there was a very simple solution to this, but unfortunately it is a little complicated, at least for a beginner.
The way glowing effects are implemented today, regardless of API (D3D,OpenGL) is with pixel/fragment-shaders. It usually involves multiple render passes where you render your scene, then render a pass where only "glowing objects" are visible, then you apply a bloom pixelshader and compose them together.
See the link provided by #Valmond for details
Edit:
It should be added that this can be achieved with deferred rendering, where normals, positions and other information like a "glow flag" is rendered to a texture, i.e. stored in different components of the texture. Then a shader will read from the textures and do lightning computations and post-processing effects in a single pass since all data it needs is available from that rendered texture.
Check this out : http://developer.download.nvidia.com/books/HTML/gpugems/gpugems_ch21.html
It explains easily how to make glow effects.
Without using shaders, you might also try rendering to texture and doing a radial blur.
As a starting point check out NeHe-Tutorials.