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POOpenGL 3 VBO Indexing Multiple figures (glDrawElements)
 

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  1. POOpenGL 3 VBO Indexing Multiple figures (glDrawElements)
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    <p>I'm working on my first steps with OpenGL (3.x) and I plan to use VAO &amp; VBO's to draw several figures (triangle, cube,...):</p> <p>Now i got the following setup:</p> <p>VAO --> VBO [vertices, colors] + VBO [indices]</p> <p>Where "vertices" has [3 * 3floats vertices of triangle, 8*3floats of cube], "colors" has RGB per vertex (no alpha), "indices" has [ triangle: 0,1,2, square: 0,1,2, 0,2,3, ...]</p> <p>Now if I draw using "glDrawElements". i only see the first figure on the series drawn correctly (and getting the right color), the second one doesn't works as it should.</p> <p>So if i render the triangle data first, it goes like:</p> <p><img src="https://i.stack.imgur.com/yKBZT.png" alt="triangle then cube"></p> <p>And if i render the cube first, it goes like:</p> <p><img src="https://i.stack.imgur.com/uBOM5.png" alt="cube then triangle"></p> <p><em>Note: triangle is red, and cube is colourful, so the first figure is always shown as I expected</em></p> <p>This worked ok drawing arrays with "glDrawArrays" (with offset + trianglecount) instead of drawElements but, of course, indexing makes the data arrays muuuuuch smaller. So i wanted to do the move.</p> <p><strong>How could i draw the same setup but with indexing? should i call another method?</strong></p> <p>This is the code I use to prepare the VBO's data, in case of doubt.</p> <pre><code>// VBOS solid glBindBuffer(GL_ARRAY_BUFFER, vboSolid[0]); glBufferData(GL_ARRAY_BUFFER, vertices.size()*sizeof(GLfloat),&amp;vertices[0], GL_STATIC_DRAW); glVertexAttribPointer((GLuint)0, 3, GL_FLOAT, GL_FALSE, 0, 0); glEnableVertexAttribArray(0); glBindBuffer(GL_ARRAY_BUFFER, vboSolid[1]); glBufferData(GL_ARRAY_BUFFER, colors.size()*sizeof(GLfloat),&amp;colors[0], GL_STATIC_DRAW); glVertexAttribPointer((GLuint)1, 3, GL_FLOAT, GL_FALSE, 0, 0); glEnableVertexAttribArray(1); glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, vboIndex ); glBufferData( GL_ELEMENT_ARRAY_BUFFER, indices.size()*sizeof(GLuint),&amp;indices[0], GL_STATIC_DRAW); glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, 0 ); </code></pre> <p>And this is the call I do when rendering. In this loop, the triangle would have indicesCount=3 &amp; offset=0, while cube would have 24 &amp; 3 respectively.</p> <pre><code>glDrawElements( GL_TRIANGLES, primitives[i]-&gt;indicesCount, GL_UNSIGNED_INT, (void*) (primitives[i]-&gt;offsetIndices*sizeof(GLuint)) ); </code></pre>
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