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POHow to apply multiple textures to a VBO of a cube?
 

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  1. POHow to apply multiple textures to a VBO of a cube?
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    <p>I'm new to VBO's and read some articles on creating and using VBO's. I am working on a application where I want to create a dozen of rotating cubes. I'm connected to a server which pushes text messages to my application. When I receive 6 text messages, I render these messages using Pango and Cairo. Then I want to create textures from these 6 rendered messages and apply those to a new Cube. </p> <p>Though I normally just use a 2D texture and apply these to a GL_QUAD, I'm not sure how I can apply 6 textures to a cube which is created using VBOs?</p> <p>I've found an example on how to create a cube using VBO. Those are created like:</p> <p><strong>The VBO</strong></p> <pre><code>// v6----- v5 // /| /| // v1------v0| // | | | | // | |v7---|-|v4 // |/ |/ // v2------v3 GLfloat vertices[] = {1,1,1, -1,1,1, -1,-1,1, 1,-1,1, // v0-v1-v2-v3 1,1,1, 1,-1,1, 1,-1,-1, 1,1,-1, // v0-v3-v4-v5 1,1,1, 1,1,-1, -1,1,-1, -1,1,1, // v0-v5-v6-v1 -1,1,1, -1,1,-1, -1,-1,-1, -1,-1,1, // v1-v6-v7-v2 -1,-1,-1, 1,-1,-1, 1,-1,1, -1,-1,1, // v7-v4-v3-v2 1,-1,-1, -1,-1,-1, -1,1,-1, 1,1,-1}; // v4-v7-v6-v5 // normal array GLfloat normals[] = {0,0,1, 0,0,1, 0,0,1, 0,0,1, // v0-v1-v2-v3 1,0,0, 1,0,0, 1,0,0, 1,0,0, // v0-v3-v4-v5 0,1,0, 0,1,0, 0,1,0, 0,1,0, // v0-v5-v6-v1 -1,0,0, -1,0,0, -1,0,0, -1,0,0, // v1-v6-v7-v2 0,-1,0, 0,-1,0, 0,-1,0, 0,-1,0, // v7-v4-v3-v2 0,0,-1, 0,0,-1, 0,0,-1, 0,0,-1}; // v4-v7-v6-v5 // color array GLfloat colors[] = {1,1,1, 1,1,0, 1,0,0, 1,0,1, // v0-v1-v2-v3 1,1,1, 1,0,1, 0,0,1, 0,1,1, // v0-v3-v4-v5 1,1,1, 0,1,1, 0,1,0, 1,1,0, // v0-v5-v6-v1 1,1,0, 0,1,0, 0,0,0, 1,0,0, // v1-v6-v7-v2 0,0,0, 0,0,1, 1,0,1, 1,0,0, // v7-v4-v3-v2 0,0,1, 0,0,0, 0,1,0, 0,1,1}; // v4-v7-v6-v5 glGenBuffersARB(1, &amp;vbo_id); glBindBufferARB(GL_ARRAY_BUFFER_ARB, vbo_id); glBufferDataARB( GL_ARRAY_BUFFER_ARB ,sizeof(vertices)+sizeof(normals)+sizeof(colors) ,0 ,GL_STATIC_DRAW_ARB ); glBufferSubDataARB(GL_ARRAY_BUFFER_ARB, 0, sizeof(vertices), vertices); glBufferSubDataARB(GL_ARRAY_BUFFER_ARB, sizeof(vertices), sizeof(normals),normals); glBufferSubDataARB(GL_ARRAY_BUFFER_ARB, sizeof(vertices)+sizeof(normals), sizeof(colors), colors); // copy colours after normals s_vertices = sizeof(vertices); s_colors = sizeof(colors); s_normals = sizeof(colors); cube = new Cube(vbo_id, ofxVec3f(0.0, 0.0, 0.0),0.1, s_vertices, s_colors, s_normals); </code></pre> <p><strong>The Cube class which uses the VBO</strong></p> <pre><code>#include "Cube.h" Cube::Cube( GLuint nVBO ,ofxVec3f oPosition ,float fSize ,int nVertices ,int nNormals ,int nColors ) :vbo_id(nVBO) ,position(oPosition) ,size(fSize) ,s_vertices(nVertices) ,s_normals(nNormals) ,s_colors(nColors) { r = 0; } void Cube::update() { } void Cube::draw() { glPushMatrix(); glTranslatef(position.x,position.y,position.z); glRotatef((r++),0,1,0); glScalef(size, size, size); // bind VBOs with IDs and set the buffer offsets of the bound VBOs // When buffer object is bound with its ID, all pointers in gl*Pointer() // are treated as offset instead of real pointer. glBindBufferARB(GL_ARRAY_BUFFER_ARB, vbo_id); // enable vertex arrays glEnableClientState(GL_NORMAL_ARRAY); glEnableClientState(GL_COLOR_ARRAY); glEnableClientState(GL_VERTEX_ARRAY); // before draw, specify vertex and index arrays with their offsets glNormalPointer(GL_FLOAT, 0, (void*)s_vertices); glColorPointer(3, GL_FLOAT, 0, (void*)(s_vertices+s_normals)); glVertexPointer(3, GL_FLOAT, 0, 0); glDrawArrays(GL_QUADS, 0, 24); glDisableClientState(GL_VERTEX_ARRAY); // disable vertex arrays glDisableClientState(GL_COLOR_ARRAY); glDisableClientState(GL_NORMAL_ARRAY); // it is good idea to release VBOs with ID 0 after use. // Once bound with 0, all pointers in gl*Pointer() behave as real // pointer, so, normal vertex array operations are re-activated glBindBufferARB(GL_ARRAY_BUFFER_ARB, 0); glPopMatrix(); } </code></pre>
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