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c++geometrypspsdkplaystation-portable

Calculate vertices of a circle

I am having a simple program, it draws a circle :/ This works fine...

for (k = 1; k < n+1+1; k++){
 vertices[k].color = GU_COLOR( 0.0f, 0.0f, 1.0f, 0.0f );
 vertices[k].x = cos_d( 360 - ((k-1) * dstep) );
 vertices[k].y = sin_d( 360 - ((k-1) * dstep) );
 vertices[k].z = 0.0f;
}
...
//Now draw it
sceGumDrawArray(GU_TRIANGLE_FAN, GU_COLOR_8888|GU_VERTEX_32BITF|GU_TRANSFORM_3D, n+1+1, 0, vertices);

But this doesn't:

for (k = 1; k < n+1+1; k++){
 vertices[k].color = GU_COLOR( 0.0f, 0.0f, 1.0f, 0.0f );
 vertices[k].x = cos_d( ((k-1) * dstep) );
 vertices[k].y = sin_d( ((k-1) * dstep) );
 vertices[k].z = 0.0f;
}

But shouldn't this be the same - just with difference that the first loop calculates the vertices clockwise and the second anti-clockwise? It's just awkward that it just doesn't draw the vertices using the second example...

Or am I stupid?

Solution

  • Not really sure how you are drawing the circle (I see you creating a list of vertices, but know nothing about the rendering of those), but:

    Usually, when you invert from clockwise to counter-clockwise, you end up getting the normal inverted, which means that you are looking at the back of your circle. And, as is the case with most APIs, when looking at the back of something (that doesn't have volume), it isn't rendered.

    This is called backface culling.