CODEWITHSUNDEEP
opengl-esopengl-es-2.0
Narek
Narek

Reputation: 39881

How many draw calls is necessary to draw a triangle fan in OpenGL ES?

I want to draw a triangle fan. I wonder if it takes 1 draw call or more. I don't think this is important, but I draw with OpenGL ES.

Upvotes: 0

Views: 193

Answers (2)

Reto Koradi
Reto Koradi

Reputation: 54572

OpenGL has a GL_TRIANGLE_FAN primitive type. So you can draw a triangle fan with a single draw call:

glDrawArrays(GL_TRIANGLE_FAN, ...);
glDrawElements(GL_TRIANGLE_FAN, ...);

The first vertex defines the "origin" of the fan. If you have n vertices for a triangle fan, there will be n - 2 triangles drawn with the following vertices:

0, 1, 2
0, 2, 3
0, 3, 4
...
0, n - 2, n - 1

Upvotes: 2

Mohit Jain
Mohit Jain

Reputation: 30489

From user point of view, you need just 1 draw call.

Internall for GPU or software renderer, this is implementation dependent whether the a particular implementation would take 1 or more draw calls.

On all GPUs known to me, we prepare just 1 draw stream which is sent to GPU and GPU draws it in 1 burst.

Upvotes: 1

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