OpenGL to OpenGL-ES - Changing color of triangles in a strip
Question
When using glBegin() and glEnd() in opengl you are able to set and change the color between each glVertex3f(). How can you recreate this behavior when using a vertex array and glDrawArrays(). Here it is in regular opengl.
for(angle = 0.0f; angle < (2.0f*GL_PI); angle += (GL_PI/8.0f))
{
// Calculate x and y position of the next vertex
x = 50.0f*sin(angle);
y = 50.0f*cos(angle);
// Alternate color between red and green
if((iPivot %2) == 0)
glColor3f(0.0f, 1.0f, 0.0f);
else
glColor3f(1.0f, 0.0f, 0.0f);
// Increment pivot to change color next time
iPivot++;
// Specify the next vertex for the triangle fan
glVertex2f(x, y);
}
Solution
With glDrawArrays you have to enable the glVertexPointer to set the vertex data.
In the same way you can also set a client-memory pointer for the colors.
It boils down to these calls:
glEnableClientState (GL_VERTEX_ARRAY);
glEnableClientState (GL_COLOR_ARRAY); // enables the color-array.
glVertexPointer (... // set your vertex-coordinates here..
glColorPointer (... // set your color-coorinates here..
glDrawArrays (... // draw your triangles
Btw - texture-coordinates are handled in the same way. Just use GL_TEXCOORD_ARRAY and glTexCoordPointer for this.
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