Sign in to follow this  

OpenGL Sphere/Cylinder mapping with OpenGL

This topic is 1751 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Hi All
I need spherical/cylindrical map for arbitrary objects (not a reflection mapping). Actually I'm calculating UV manually. If a polygon crosses UV seam or pole, then I split it into several new polygons. It works but it's a big piece of code that makes app much slower. Are there better ways with OpenGL?

Share this post

Link to post
Share on other sites

Tbh, I don't know the exact algorithms used to do this, but I have managed to do this (at least the spherical) in OpenGL by copying some code from the DirectX 9 SDK (the older ones)  and changing the necessary features to work for OpenGL.  It's been years since I've done this so I can't remember exactly what I changed for the sphere, but it should be obvious enough IMO.


Here's the sphere: 

// Establish constants used in sphere generation
    DWORD dwNumSphereRings    = m_bHighTesselation ? 15 :  5;
    DWORD dwNumSphereSegments = m_bHighTesselation ? 30 : 10;
    FLOAT fDeltaRingAngle = ( D3DX_PI / dwNumSphereRings );
    FLOAT fDeltaSegAngle  = ( 2.0f * D3DX_PI / dwNumSphereSegments );

    FLOAT fScale;

    // Generate the group of rings for the sphere
    for( DWORD ring = 0; ring < (dwNumSphereRings/2); ring++ )
        FLOAT r0 = sinf( (ring+0) * fDeltaRingAngle );
        FLOAT r1 = sinf( (ring+1) * fDeltaRingAngle );
        FLOAT y0 = cosf( (ring+0) * fDeltaRingAngle );
        FLOAT y1 = cosf( (ring+1) * fDeltaRingAngle );

        // Generate the group of segments for the current ring
        for( DWORD seg = 0; seg < (dwNumSphereSegments+1); seg++ )
            FLOAT x0 =  r0 * sinf( seg * fDeltaSegAngle );
            FLOAT z0 =  r0 * cosf( seg * fDeltaSegAngle );
            FLOAT x1 =  r1 * sinf( seg * fDeltaSegAngle );
            FLOAT z1 =  r1 * cosf( seg * fDeltaSegAngle );

            // Add two vertices to the strip which makes up the sphere
            // (using the transformed normal to generate texture coords)
            (*vtx).p   = (*vtx).n   = D3DXVECTOR3(x0,y0,z0);
            D3DXVec3Transform( &vT, &(*vtx).n, &matWorldView );
            fScale = 1.37f / D3DXVec4Length( &vT );
            (*vtx).tu1 = 0.5f + fScale*vT.x;
            (*vtx).tv1 = 0.5f - fScale*vT.y;

            (*vtx).p   = (*vtx).n   = D3DXVECTOR3(x1,y1,z1);
            D3DXVec3Transform( &vT, &(*vtx).n, &matWorldView );
            fScale = 1.37f / D3DXVec4Length( &vT );
            (*vtx).tu1 = 0.5f + fScale*vT.x;
            (*vtx).tv1 = 0.5f - fScale*vT.y;


Then draw as a triangle strip.  You'll have to use your own matrix transformation and vector length functions to do the texture coordinates, but that shouldn't be hard.


The cylinder is much easier.  I don't know if you want an open or closed cylinder, I've never done the latter.

for( DWORD i=0; i<50; i++ )
        FLOAT theta = (2*D3DX_PI*i)/(50-1);

        pVertices[2*i+0].position = D3DXVECTOR3( sinf(theta),-1.0f, cosf(theta) );
        pVertices[2*i+0].color    = 0xffffffff;
        pVertices[2*i+0].tu       = ((FLOAT)i)/(50-1);
        pVertices[2*i+0].tv       = 1.0f;

        pVertices[2*i+1].position = D3DXVECTOR3( sinf(theta), 1.0f, cosf(theta) );
        pVertices[2*i+1].color    = 0xff808080;
        pVertices[2*i+1].tu       = ((FLOAT)i)/(50-1);
        pVertices[2*i+1].tv       = 0.0f;


Then draw as a triangle strip.  This example uses 100 vertices btw.


Not sure if this helped, but I tried. smile.png



Share this post

Link to post
Share on other sites

blueshougun96. thx for your reply. I've no problems with UV calculation itself, my question was about "should I do that" or, in other words. "can I avoid manual UV calcs?". An answer "no, you can't"  would be also informative for me, if so I'm doing things right




Edited by Tommato

Share this post

Link to post
Share on other sites

Okay, my mistake.  


Generally speaking, it should be fine, that's what I'd do.  I don't know of any way to do it automatically, unless OpenGL has an equivalent of D3DTSS_TCI_x.  



Share this post

Link to post
Share on other sites

This topic is 1751 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Similar Content

    • By xhcao
      Does sync be needed to read texture content after access texture image in compute shader?
      My simple code is as below,
      glBindImageTexture(0, texture[0], 0, GL_FALSE, 3, GL_READ_ONLY, GL_R32UI);
      glBindImageTexture(1, texture[1], 0, GL_FALSE, 4, GL_WRITE_ONLY, GL_R32UI);
      glDispatchCompute(1, 1, 1);
      // Does sync be needed here?
      glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
                                     GL_TEXTURE_CUBE_MAP_POSITIVE_X + face, texture[1], 0);
      glReadPixels(0, 0, kWidth, kHeight, GL_RED_INTEGER, GL_UNSIGNED_INT, outputValues);
      Compute shader is very simple, imageLoad content from texture[0], and imageStore content to texture[1]. Does need to sync after dispatchCompute?
    • By Jonathan2006
      My question: is it possible to transform multiple angular velocities so that they can be reinserted as one? My research is below:
      // This works quat quaternion1 = GEQuaternionFromAngleRadians(angleRadiansVector1); quat quaternion2 = GEMultiplyQuaternions(quaternion1, GEQuaternionFromAngleRadians(angleRadiansVector2)); quat quaternion3 = GEMultiplyQuaternions(quaternion2, GEQuaternionFromAngleRadians(angleRadiansVector3)); glMultMatrixf(GEMat4FromQuaternion(quaternion3).array); // The first two work fine but not the third. Why? quat quaternion1 = GEQuaternionFromAngleRadians(angleRadiansVector1); vec3 vector1 = GETransformQuaternionAndVector(quaternion1, angularVelocity1); quat quaternion2 = GEQuaternionFromAngleRadians(angleRadiansVector2); vec3 vector2 = GETransformQuaternionAndVector(quaternion2, angularVelocity2); // This doesn't work //quat quaternion3 = GEQuaternionFromAngleRadians(angleRadiansVector3); //vec3 vector3 = GETransformQuaternionAndVector(quaternion3, angularVelocity3); vec3 angleVelocity = GEAddVectors(vector1, vector2); // Does not work: vec3 angleVelocity = GEAddVectors(vector1, GEAddVectors(vector2, vector3)); static vec3 angleRadiansVector; vec3 angularAcceleration = GESetVector(0.0, 0.0, 0.0); // Sending it through one angular velocity later in my motion engine angleVelocity = GEAddVectors(angleVelocity, GEMultiplyVectorAndScalar(angularAcceleration, timeStep)); angleRadiansVector = GEAddVectors(angleRadiansVector, GEMultiplyVectorAndScalar(angleVelocity, timeStep)); glMultMatrixf(GEMat4FromEulerAngle(angleRadiansVector).array); Also how do I combine multiple angularAcceleration variables? Is there an easier way to transform the angular values?
    • By dpadam450
      I have this code below in both my vertex and fragment shader, however when I request glGetUniformLocation("Lights[0].diffuse") or "Lights[0].attenuation", it returns -1. It will only give me a valid uniform location if I actually use the diffuse/attenuation variables in the VERTEX shader. Because I use position in the vertex shader, it always returns a valid uniform location. I've read that I can share uniforms across both vertex and fragment, but I'm confused what this is even compiling to if this is the case.
      #define NUM_LIGHTS 2
      struct Light
          vec3 position;
          vec3 diffuse;
          float attenuation;
      uniform Light Lights[NUM_LIGHTS];
    • By pr033r
      I have a Bachelor project on topic "Implenet 3D Boid's algorithm in OpenGL". All OpenGL issues works fine for me, all rendering etc. But when I started implement the boid's algorithm it was getting worse and worse. I read article ( inspirate from another code (here: but it still doesn't work like in tutorials and videos. For example the main problem: when I apply Cohesion (one of three main laws of boids) it makes some "cycling knot". Second, when some flock touch to another it scary change the coordination or respawn in origin (x: 0, y:0. z:0). Just some streng things. 
      I followed many tutorials, change a try everything but it isn't so smooth, without lags like in another videos. I really need your help. 
      My code (optimalizing branch):
      Exe file (if you want to look) and models folder (for those who will download the sources):
      Thanks for any help...

    • By Andrija
      I am currently trying to implement shadow mapping into my project , but although i can render my depth map to the screen and it looks okay , when i sample it with shadowCoords there is no shadow.
      Here is my light space matrix calculation
      mat4x4 lightViewMatrix; vec3 sun_pos = {SUN_OFFSET * the_sun->direction[0], SUN_OFFSET * the_sun->direction[1], SUN_OFFSET * the_sun->direction[2]}; mat4x4_look_at(lightViewMatrix,sun_pos,player->pos,up); mat4x4_mul(lightSpaceMatrix,lightProjMatrix,lightViewMatrix); I will tweak the values for the size and frustum of the shadow map, but for now i just want to draw shadows around the player position
      the_sun->direction is a normalized vector so i multiply it by a constant to get the position.
      player->pos is the camera position in world space
      the light projection matrix is calculated like this:
      mat4x4_ortho(lightProjMatrix,-SHADOW_FAR,SHADOW_FAR,-SHADOW_FAR,SHADOW_FAR,NEAR,SHADOW_FAR); Shadow vertex shader:
      uniform mat4 light_space_matrix; void main() { gl_Position = light_space_matrix * transfMatrix * vec4(position, 1.0f); } Shadow fragment shader:
      out float fragDepth; void main() { fragDepth = gl_FragCoord.z; } I am using deferred rendering so i have all my world positions in the g_positions buffer
      My shadow calculation in the deferred fragment shader:
      float get_shadow_fac(vec4 light_space_pos) { vec3 shadow_coords = / light_space_pos.w; shadow_coords = shadow_coords * 0.5 + 0.5; float closest_depth = texture(shadow_map, shadow_coords.xy).r; float current_depth = shadow_coords.z; float shadow_fac = 1.0; if(closest_depth < current_depth) shadow_fac = 0.5; return shadow_fac; } I call the function like this:
      get_shadow_fac(light_space_matrix * vec4(position,1.0)); Where position is the value i got from sampling the g_position buffer
      Here is my depth texture (i know it will produce low quality shadows but i just want to get it working for now):
      sorry because of the compression , the black smudges are trees ...
      EDIT: Depth texture attachment:
  • Popular Now