Question

I’m new to OpenGl ES. I’m trying to build a sphere not using any manuals, tutrials…

I have succeded to achieve my goal. I can draw a sphere using TRIANGLE_STRIP. And the number of meridians/horizontals I specify before drawing.

Everything works fine when I have less then 256 indexes for vertixes. I tried to use GLushort instead of GLubyte but the picture changed a lot.

GLubyte *Indices;
...
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLubyte) * (meridians * (horizontals * 2 + 2)), Indices, GL_STATIC_DRAW);
...
Indices = malloc(sizeof(GLubyte) * (meridians * (horizontals * 2 + 2)));

Thats where I change byte to short.

Current project on GitHub

What should I do?

Here are the pictures where I change byte to short

Answer 1

Looks like you forgot to change the following line:

glDrawElements(GL_TRIANGLE_STRIP, (meridians * (horizontals * 2 + 2)), GL_UNSIGNED_BYTE, 0);

This indicates that there are a number of indices to be render, and each one is the size of an unsigned byte (most likely 8 bits, but the actual number is platform specific…very very very rarely is it not 8 bits though). However, you have filled an array of indices that are the size of unsigned shorts (probably 16 bits) so what will end up happening is that each of your numbers will be read twice. Once with the “first” 8-bits, and once with the “second” (endian will determine whether high or low order comes first). Since a lot of your indices (the majority?) are under 255, then there are going to be a lot of vertices that turn into “0” since the higher 8 bits are all 0. On top of that, you will only render half of your indices.

So, you need to indicate to OpenGL that it needs to draw these indices as unsigned shorts instead by changing the above line to this:

glDrawElements(GL_TRIANGLE_STRIP, (meridians * (horizontals * 2 + 2)), GL_UNSIGNED_SHORT, 0);