Is there an alternative to VBOs or deprecated functions to draw many small quads?

Question

I was thinking about how to program a user interface in a 3D game. The problem is, immediate mode (glBegin and glEnd) is deprecated for a long time but I don't think vertex buffer objects (or arrays) are needed just for the (2D) quads I want to draw (and I don't think they are even efficient for plenty of small quads).

Are there any approaches on how to avoid vertex-buffer-objects/arrays and the deprecated functions?

Answer 1

Not really. Use vertex buffer objects. There can be perfectly efficient for large numbers of small triangles.

The thing is that you don't want to make one VBO per quad, but rather few VBOs into which you stuff multiple quads.

Answer 2

You can use instancing and a texture atlas to combine all the draw calls into a single one.

You only have a single 4 vertex VBO with the 4 corners 0,0 0,1 1,1 1,0 and an index buffer to draw them using GL_TRIANGLES.

Then in a separate VBO you have the position and size of the quad (in a single vec4) and the position and size of the texture to use in the atlas (again as a vec4).

in vec2 coords;

in vec4 location;//x and y is the relative offset and z and w is the scaling factor
in vec4 textureLoc;

out vec2 texCoord;//0-1 as you would without the atlas

main(){
   gl_Position = coords.xy*location.zw + location.xy;
   texCoord = coords.xy*textureLoc.zw + textureLoc.xy;
}

Then during the rendering you fill the second VBO with position, size, texturePosition, textureSize, set the attribute pointer as if they where one for each vertex and set the attribute Divisor to 1; draw with

void glDrawElementsInstanced​(GL_TRIANGLES​, 6, GL_Int, 0​, numberQuads);