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In the OpenGL ES 2.0 introduction, found here: http://www.webreference.com/programming/opengl_es/2.html a vertex shader is defined: GLbyte vShaderStr[] = "attribute vec4 vPosition; \n" "void main() \n" "{ \n" " gl_Position = vPosition; \n" "}; \n"; The vPosition attribute is a four component vector. Later in the text the application will compile the vertex shader, together with the fragment shader. With the glBindAttribLocation a handle to pass the applications vertex data to the shader is established: // Bind vPosition to attribute 0 glBindAttribLocation(programObject, 0, "vPosition"); The 2 shaders are now linked and the program is ready to use. The use case is this: GLfloat vVertices[] = {0.0f, 0.5f, 0.0f, -0.5f, -0.5f, 0.0f, 0.5f, -0.5f, 0.0f}; ... // Load the vertex data glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, vVertices); glEnableVertexAttribArray(0); glDrawArrays(GL_TRIANGLES, 0, 3); Which means: glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, vVertices) : pass the vertex data to the program, use location 0, each vertex has 3 components, type is float, no normalisation shall be used. glEnableVertexAttribArray(0) : The shader will use the passed data. glDrawArrays(GL_TRIANGLES, 0, 3); : The shader will execute the code to draw a single triangle, using the first (and only) three vertices found in the specified array. My Questions are: The vertex shader is expecting a four component vertex position (x,y,z,w), the program passes only three components (x,y,z) data Why is this working?

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