2D shape using OpenGL

[Henan Zhao]

Hi,

I'd like to draw a 2D shape on the screen using OpenGL.

I tried to use gluUnProject, but I cannot get the correct coordinates of the objects. Also, if I drew a horizontal line, the line has the slope instead of a horizontal one.
Our cave is the part of one cylinder, maybe 1/4.

Could you please help me about that?

Thanks a lot.

[Alessandro Febretti]

Hi Henan,

what are you doing exactly to draw in 2D?

the correct way is to do it inside a renderpass render method, on the OverlayDrawTask draw phase. During that render call, the draw context passed to the render method contains all the information you need to set up 2D drawing.

You basically want to do:

YourRenderPass::render(DrawContext& context)
{
    if(context.task == DrawContext::OverlayDrawtask && context.eye == DrawContext::EyeCyclop)
    {
 DrawInterface* di = getClient()->getRenderer();
 di->beginDraw2D(context);
// Do your drawing here
di->endDraw();
    }
}

An example of this here: https://github.com/uic-evl/omegalib/blob/master/src/omega/Console.cpp#L189

An important note: beginDraw2D only works on OpenGL compatibility profiles since it uses legacy openGL functions to pass the transforms to the render pipeline. If you run omegalib with coreProfile = true; in the display section to request a forward-compatible openGL profile, that call won't  do anything and you will have to pass the transforms to your shaders manually. An example of 2D drawing fully compatible with modern OpenGL is here: https://github.com/omega-hub/overlay/blob/master/overlay.cpp

[Henan Zhao]

Hi Alessandro,

Thanks.

I have a new problem. Can you please give me some example how I can integrate 2D and 3D visualization? 

For example, I have a 2D image, or some basic shapes like 2D rectangles and circles and also 3D visualization, like volume rendering. 

Is it possible that both SceneDrawTask and OverlayDrawtask co-exist in one render pass?

Thank you very much.

Henan

[Alessandro Febretti]

Yes you can render 3D (in a scene render pass) and 2D (in an overlay render pass).

The widgets in the OmegaToolkit UI are rendered this way.

You can also check the on-screen console rendering code https://github.com/uic-evl/omegalib/blob/master/src/omega/Console.cpp

Or this overlay rendering module (designed for OpenGL 4 forward profiles) https://github.com/omega-hub/overlay/blob/master/overlay.cpp

[Henan Zhao]

Hi Alessandro,

Thanks a lot.
I haven't tried that but will do that soon.

Thank you again.
Henan