Fastest way to draw quads in OpenGL ES?

Question

I am using OpenGL ES 2.0 I have a bunch a quads to be drawn, would love to be able to have to pass only 4 vertices per quad as if I were using GL_QUADS, but basically I just want to know the best way of drawing a bunch of separate quads.

So far what I've found I could do: -GL_TRIANGLES(6 vertices per quad) -Degenerate GL_TRIANGLE_STRIP(6 vertices per quad)

Possibities I've found: -GL_TRIANGLE_STRIPS with a special index value that resets quad strip(this would mean 5 indexes per quad, but I dont think this is possible is OpenGL ES 2.0)

Answer 1

Just use index buffer and GL_TRIANGLES. In this case you need 4 vertices + 6 indices per quad (6 additional indices may sound large overhead but in reality it is not - once you have constructed your index buffer you don't have to touch it again). See this page for more information (search for glDrawElements)

Simple example code:

GLfloat vertices[] = {-1, -1, 0, //bottom left corner
                      -1,  1, 0, //top left corner
                       1,  1, 0, //top right corner
                       1, -1, 0}; // bottom right rocner

GLubyte indices[] = {0,1,2, // first triangle (bottom left - top left - top right)
                     0,2,3}; // second triangle (bottom left - top right - bottom right)

glVertexPointer(3, GL_FLOAT, 0, vertices);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_BYTE, indices);

Also, if you are drawing just one quad you need only 4 vertices to draw it with triangle strips (as shown in wikipedia) but I guess you already knew this.

Answer 2

A GL_TRIANGLE_STRIP will do it in 4 vertices, without needing an index buffer, but if you're drawing more than 1 quad, I'd say to go with the index buffer method.

To steal/adapt from the accepted answer:

GLfloat vertices[] = {-1, -1, 0, //bottom left corner
                       1, -1, 0, //CHANGED! order bottom right "rocner"
                      -1,  1, 0, //top left corner
                       1,  1, 0, //top right corner
                     };

// Create and bind the vertex buffer...

// 2----3
// | \  |
// |  \ |
// 0----1
glDrawArrays( GL_TRIANGLE_STRIP, 0, 4 ) ;

Answer 3

The big gain on desktop is to move the data into GL_STATIC_DRAW VBOs. Presumably this is true on iPhone's MBX GPU too.