Where are the draw calls of the OpenGL backend?

[PucklaJ]

First I want to say: Thank you for this amazing library. This is exactly what I need.

I want to use this library with OpenGL to render a GUI. I would like to have hardware acceleration which draw2d provides via draw2dgl. But this backend is implemented in OpenGL 1.0 and therefore you are limited to a Context of OpenGL 2.1 at max. If you want to have nice shader effects or if your hardware does not support immediate mode rendering, you have a problem. Therefore I would like to port the OpenGL backend to OpenGL ES 2 to also get better support on ARM SoCs. Now I am wondering: Where is the code that actually calls OpenGL? All I can find are a few lines in gc.go that render lines. But where are the triangles getting rendered?

This information would be very appreciated.

[PucklaJ]

raster.Span

// A Span is a horizontal segment of pixels with constant alpha. X0 is an
// inclusive bound and X1 is exclusive, the same as for slices. A fully opaque
// Span has Alpha == 0xffff.
type Span struct {
	Y, X0, X1 int
	Alpha     uint32
}

I did some research and found out that the draw2dgl.Painter is rendering raster.Span elements. If I understand correctly, a CPU rasterizer first creates horizontal lines out of filled geometry and then those lines are rendered using a line renderer in OpenGL. This seems to be very inefficient, since OpenGL can rasterize geometry on the GPU. Maybe I will use draw2d only for text rendering and create my own shape renderer. But at least this answers my question.

I will keep this issue open, in case someone wants to comment on this. Feel free to close it.

[llgcode]

Hi @PucklaJ,
Yes the gl renderer is not efficient at all it needs to be rewritten. It was an experimentation.