Thick Outlines

OpenGL OpenGL: Basic Coding
1

I´m trying to draw 2D figures with a thick outline.

I tried to draw them with PolygonOffset and also with the Stencil buffer, but as the outline gets thicker it looses it´s smoothness and starts to look as a sequence of rectangles.

Is there any other method to draw 2D figures with a thick outline?

Thanks in advance

Gabriel

2

Yes. Couldn’t resist. :wink:

You could render the outline as QuadStrip generating a mitered wide line, but you need to be very careful about the vertex placements in that strip.

Here’s a really nice but advanced method:
http://www2.imm.dtu.dk/pubdb/views/edoc_download.php/4884/pdf/imm4884.pdf

3

Another option is to use the stencil buffer to render an outline and them blur the outline a little to make it thicker. This is probably a slower than the previous method mentioned but it was the first alternative I could think of.

4

Thanks for the responses, but they seem far ahead of my possibilities (i´m a newbie by all means).

With glPolygonOffset I drew the outline first and the solid polygon last and it worked ok (except that i had the problem described in my previous post)

Now i´m trying to draw the polygon with glPolygonOffset twice. First with some offset to make it bigger, and then as is.

But no matter what i pass to glPolygonOffset, I cannot make the bigger polygon appear.

I´m trying something like this:

glEnable(GL_POLYGON_OFFSET_FILL);
glEnable(GL_DEPTH_TEST);
glDisable(GL_CULL_FACE);

glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
glPolygonOffset(//any value, //any value);

//draw blue bigger polygon

glDisable(GL_POLYGON_OFFSET_FILL);
glDisable(GL_DEPTH_TEST);

//draw red polygon

Thanks

Gabriel