# OpenGL 'Holes' with Procedurally Generated Sphere for OpenGL

## Recommended Posts

tmason    326

Hello,

Hopefully this is a simple question; I have the following code that I am using to generate a sphere object for OpenGL. The problem is, as the picture will show, is that there are "holes" in the spheres. I placed a few boxes in the scene to show that overall my buffers/shaders seem to be OK and I believe the problem may be the indices.

Anyway, here is the picture:

And here is how I am generating the sphere:

float ShapeRadius = 3.0f;

GLuint NumberOfRings = 50;
GLuint NumberOfSectors = 50;

float const R = 1. / (GLfloat)(NumberOfRings - 1);
float const S = 1. / (GLfloat)(NumberOfSectors - 1);

int r, s;

Temp_Vertices = new std::vector<GLfloat>;
Temp_Normals = new std::vector<GLfloat>;
Temp_TextCoords = new std::vector<GLfloat>;

Temp_Indices = new std::vector<GLuint>;

Temp_Vertices->resize(NumberOfRings * NumberOfSectors * 3);
Temp_Normals->resize(NumberOfRings * NumberOfSectors * 3);
Temp_TextCoords->resize(NumberOfRings * NumberOfSectors * 2);

std::vector<GLfloat>::iterator v = Temp_Vertices->begin();
std::vector<GLfloat>::iterator n = Temp_Normals->begin();
std::vector<GLfloat>::iterator t = Temp_TextCoords->begin();

for (r = 0; r < NumberOfRings; r++) for (s = 0; s < NumberOfSectors; s++) {

float const y = sin(-M_PI_2 + M_PI * r * R);
float const x = cos(2 * M_PI * s * S) * sin(M_PI * r * R);
float const z = sin(2 * M_PI * s * S) * sin(M_PI * r * R);

*t++ = s*S;
*t++ = r*R;

*n++ = x;
*n++ = y;
*n++ = z;
}

Temp_Indices->resize(NumberOfRings * NumberOfSectors * 4);

std::vector<GLuint>::iterator i = Temp_Indices->begin();

for (r = 0; r < NumberOfRings; r++) for (s = 0; s < NumberOfSectors; s++) {
*i++ = r * NumberOfSectors + s;
*i++ = r * NumberOfSectors + (s + 1);
*i++ = (r + 1) * NumberOfSectors + (s + 1);
*i++ = (r + 1) * NumberOfSectors + s;
}
Vertices = Temp_Vertices->data();
NumOfVertices = Temp_Vertices->size();

Indices = Temp_Indices->data();
NumOfIndices = Temp_Indices->size();

Normals = Temp_Normals->data();
NumOfNormals = Temp_Normals->size();

TextureCoordinates = Temp_TextCoords->data();
NumOfTextureCoordinates = Temp_TextCoords->size();


What can I do to get rid of the holes?

Thank you.

##### Share on other sites

the picture is not present so i can just guess.if you are culling front face then the end of your rings are drawn as back face so they're not shown

##### Share on other sites
Erik Rufelt    5901

Start by breaking out of the loop early, first after the first iteration, then after the second, and so on, for both the sectors and the ring.

That should go from no polygons to a single triangle at the top of the sphere, and then if that looks OK then go to a full ring, and when that looks OK go to 2 rings.

It should make it much easier to isolate the problem, than trying to see why the full sphere looks like it does.

In this case I'm reasonably sure your problem is in building the indices. Are you drawing with GL_TRIANGLES?

If so you need 6 indices per quad, as it's built from 2 separate triangles. From your indices you need to draw a separate quad or triangle-strip for each sector.

If it still looks strange, do glDisable(GL_CULL_FACE) and see if it fixes it, which would mean face-winding is inverted.

##### Share on other sites
alh420    5995

The problem definitely is the indices (all the points seem to be in the right place)

It looks like you are generating quads, but are drawing it as triangles, as Erik suspects.

Edited by Olof Hedman

##### Share on other sites
Rootus    851

After executing your code I think the problem is indeed in drawing 'GL_QUADS' geometry with 'GL_TRIANGLES'. Take a look at the following screenshots of your geometry.

[attachment=23463:Triangles_BackfaceCulling.jpg] Fig.1. Drawing with GL_TRIANGLES and GL_CULL_FACE enabled.

[attachment=23464:Triangles.jpg] Fig.2. Drawing with GL_TRIANGLES and GL_CULL_FACE disabled.

##### Share on other sites
tmason    326

Start by breaking out of the loop early, first after the first iteration, then after the second, and so on, for both the sectors and the ring.
That should go from no polygons to a single triangle at the top of the sphere, and then if that looks OK then go to a full ring, and when that looks OK go to 2 rings.
It should make it much easier to isolate the problem, than trying to see why the full sphere looks like it does.

In this case I'm reasonably sure your problem is in building the indices. Are you drawing with GL_TRIANGLES?
If so you need 6 indices per quad, as it's built from 2 separate triangles. From your indices you need to draw a separate quad or triangle-strip for each sector.
If it still looks strange, do glDisable(GL_CULL_FACE) and see if it fixes it, which would mean face-winding is inverted.

Changing to GL_QUADS per @Rootus's suggestion worked! Thanks.

One problem though; on Intel-based systems I get the sphere with no problems but on AMD based graphics cards nothing shows up.

I haven't tried the code on nVidia based systems.

Any reason why this may be?

##### Share on other sites
tmason    326

After executing your code I think the problem is indeed in drawing 'GL_QUADS' geometry with 'GL_TRIANGLES'. Take a look at the following screenshots of your geometry.

Triangles_BackfaceCulling.jpg Fig.1. Drawing with GL_TRIANGLES and GL_CULL_FACE enabled.

Triangles.jpg Fig.2. Drawing with GL_TRIANGLES and GL_CULL_FACE disabled.

Thank you for trying this out!

Hope to get this fully working on all systems like AMD.

So far I only see stuff on Intel...

##### Share on other sites
TheChubu    9446

One problem though; on Intel-based systems I get the sphere with no problems but on AMD based graphics cards nothing shows up.

If you're using 'core' profile, GL_QUADS is deprecated. That might be why AMD driver refuses to draw anything. The solution would be to add the indices for the missing triangle for each quad you're generating (and draw with GL_TRIANGLES).

Edited by TheChubu

## Create an account

Register a new account

• ### Similar Content

• I'm trying to get some legacy OpenGL code to run with a shader pipeline,
The legacy code uses glVertexPointer(), glColorPointer(), glNormalPointer() and glTexCoordPointer() to supply the vertex information.
I know that it should be using setVertexAttribPointer() etc to clearly define the layout but that is not an option right now since the legacy code can't be modified to that extent.
I've got a version 330 vertex shader to somewhat work:
#version 330 uniform mat4 osg_ModelViewProjectionMatrix; uniform mat4 osg_ModelViewMatrix; layout(location = 0) in vec4 Vertex; layout(location = 2) in vec4 Normal; // Velocity layout(location = 3) in vec3 TexCoord; // TODO: is this the right layout location? out VertexData { vec4 color; vec3 velocity; float size; } VertexOut; void main(void) { vec4 p0 = Vertex; vec4 p1 = Vertex + vec4(Normal.x, Normal.y, Normal.z, 0.0f); vec3 velocity = (osg_ModelViewProjectionMatrix * p1 - osg_ModelViewProjectionMatrix * p0).xyz; VertexOut.velocity = velocity; VertexOut.size = TexCoord.y; gl_Position = osg_ModelViewMatrix * Vertex; } What works is the Vertex and Normal information that the legacy C++ OpenGL code seem to provide in layout location 0 and 2. This is fine.
What I'm not getting to work is the TexCoord information that is supplied by a glTexCoordPointer() call in C++.
Question:
What layout location is the old standard pipeline using for glTexCoordPointer()? Or is this undefined?

Side note: I'm trying to get an OpenSceneGraph 3.4.0 particle system to use custom vertex, geometry and fragment shaders for rendering the particles.

• Hi i am new to this forum  i wanted to ask for help from all of you i want to generate real time terrain using a 32 bit heightmap i am good at c++ and have started learning Opengl as i am very interested in making landscapes in opengl i have looked around the internet for help about this topic but i am not getting the hang of the concepts and what they are doing can some here suggests me some good resources for making terrain engine please for example like tutorials,books etc so that i can understand the whole concept of terrain generation.

• By KarimIO
Hey guys. I'm trying to get my application to work on my Nvidia GTX 970 desktop. It currently works on my Intel HD 3000 laptop, but on the desktop, every bind textures specifically from framebuffers, I get half a second of lag. This is done 4 times as I have three RGBA textures and one depth 32F buffer. I tried to use debugging software for the first time - RenderDoc only shows SwapBuffers() and no OGL calls, while Nvidia Nsight crashes upon execution, so neither are helpful. Without binding it runs regularly. This does not happen with non-framebuffer binds.
GLFramebuffer::GLFramebuffer(FramebufferCreateInfo createInfo) { glGenFramebuffers(1, &fbo); glBindFramebuffer(GL_FRAMEBUFFER, fbo); textures = new GLuint[createInfo.numColorTargets]; glGenTextures(createInfo.numColorTargets, textures); GLenum *DrawBuffers = new GLenum[createInfo.numColorTargets]; for (uint32_t i = 0; i < createInfo.numColorTargets; i++) { glBindTexture(GL_TEXTURE_2D, textures[i]); GLint internalFormat; GLenum format; TranslateFormats(createInfo.colorFormats[i], format, internalFormat); // returns GL_RGBA and GL_RGBA glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, createInfo.width, createInfo.height, 0, format, GL_FLOAT, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); DrawBuffers[i] = GL_COLOR_ATTACHMENT0 + i; glBindTexture(GL_TEXTURE_2D, 0); glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + i, textures[i], 0); } if (createInfo.depthFormat != FORMAT_DEPTH_NONE) { GLenum depthFormat; switch (createInfo.depthFormat) { case FORMAT_DEPTH_16: depthFormat = GL_DEPTH_COMPONENT16; break; case FORMAT_DEPTH_24: depthFormat = GL_DEPTH_COMPONENT24; break; case FORMAT_DEPTH_32: depthFormat = GL_DEPTH_COMPONENT32; break; case FORMAT_DEPTH_24_STENCIL_8: depthFormat = GL_DEPTH24_STENCIL8; break; case FORMAT_DEPTH_32_STENCIL_8: depthFormat = GL_DEPTH32F_STENCIL8; break; } glGenTextures(1, &depthrenderbuffer); glBindTexture(GL_TEXTURE_2D, depthrenderbuffer); glTexImage2D(GL_TEXTURE_2D, 0, depthFormat, createInfo.width, createInfo.height, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glBindTexture(GL_TEXTURE_2D, 0); glFramebufferTexture(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, depthrenderbuffer, 0); } if (createInfo.numColorTargets > 0) glDrawBuffers(createInfo.numColorTargets, DrawBuffers); else glDrawBuffer(GL_NONE); if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) std::cout << "Framebuffer Incomplete\n"; glBindFramebuffer(GL_FRAMEBUFFER, 0); width = createInfo.width; height = createInfo.height; } // ... // FBO Creation FramebufferCreateInfo gbufferCI; gbufferCI.colorFormats = gbufferCFs.data(); gbufferCI.depthFormat = FORMAT_DEPTH_32; gbufferCI.numColorTargets = gbufferCFs.size(); gbufferCI.width = engine.settings.resolutionX; gbufferCI.height = engine.settings.resolutionY; gbufferCI.renderPass = nullptr; gbuffer = graphicsWrapper->CreateFramebuffer(gbufferCI); // Bind glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo); // Draw here... // Bind to textures glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, textures[0]); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, textures[1]); glActiveTexture(GL_TEXTURE2); glBindTexture(GL_TEXTURE_2D, textures[2]); glActiveTexture(GL_TEXTURE3); glBindTexture(GL_TEXTURE_2D, depthrenderbuffer); Here is an extract of my code. I can't think of anything else to include. I've really been butting my head into a wall trying to think of a reason but I can think of none and all my research yields nothing. Thanks in advance!

• Hi everyone, I've shared my 2D Game Engine source code. It's the result of 4 years working on it (and I still continue improving features ) and I want to share with the community. You can see some videos on youtube and some demo gifs on my twitter account.
This Engine has been developed as End-of-Degree Project and it is coded in Javascript, WebGL and GLSL. The engine is written from scratch.
This is not a professional engine but it's for learning purposes, so anyone can review the code an learn basis about graphics, physics or game engine architecture. Source code on this GitHub repository.
I'm available for a good conversation about Game Engine / Graphics Programming
• By C0dR
I would like to introduce the first version of my physically based camera rendering library, written in C++, called PhysiCam.
Physicam is an open source OpenGL C++ library, which provides physically based camera rendering and parameters. It is based on OpenGL and designed to be used as either static library or dynamic library and can be integrated in existing applications.

The following features are implemented:
Physically based sensor and focal length calculation Autoexposure Manual exposure Lense distortion Bloom (influenced by ISO, Shutter Speed, Sensor type etc.) Bokeh (influenced by Aperture, Sensor type and focal length) Tonemapping
You can find the repository at https://github.com/0x2A/physicam

I would be happy about feedback, suggestions or contributions.

• 10
• 10
• 18
• 9
• 9