kicad-developers team mailing list archive

[Maciej Sumiński <maciej.suminski@xxxxxxx>]

On 02/24/2014 08:45 AM, Lorenzo Marcantonio wrote:
> > - Handling a VBO for line strips (and probably a shader or some other way of
> > controlling line width per line, not for the whole batch). I am not sure if
> > degenerated vertices (i.e. two consecutives vertices with the same
> > coordinates to indicate beginning of a new line) work in GL_LINE_STRIP mode,
> > otherwise you have to use GL_LINE instead.
>
> Text should never generate identical vertices, otherwise font data is
> misoptimized :P anyway I don't remember seeing something forbidding them
> (but also nothing guaranteeing... so maybe they are implementation
> dependant - as usual!)

It is not that text should generate identical vertices, the purpose is 
to separate lines stored in a single VBO. If you have a VBO drawn as 
GL_LINE_STRIP, then you will have *all* vertices drawn as a single 
continous line, so you need a way to tell GPU that there should be a 
break. It is better explained here (for triangles), chapter "Use 
Triangle Strips to Batch Vertex Data":
https://developer.apple.com/library/ios/DOCUMENTATION/3DDrawing/Conceptual/OpenGLES_ProgrammingGuide/TechniquesforWorkingwithVertexData/TechniquesforWorkingwithVertexData.html

> Using a shader to fix line width should work, but doesn't reduce vertex
> count. I hoped to do that. Also I have no idea on how shaders work :P
>
> > - Drawing using direct mode, but in this case all lines should be drawn at
> > the same time. Also I wonder how does it compete with current VBO batch in
> > terms of performance.
> > If I had to choose, I would go for bitmap fonts. It makes every character
> > one quad or two triangles. Or maybe antialiasing could solve the problem?
>
> Texturing the font would need a) a huge amount of texture memory (and
> Intels are sharing the system memory) and b) losing crispness due to
> resampling; I'd prefer the current situation in that case :D

a) Why do you think so? It is just one black & white texture containing 
all characters (e.g. http://i.stack.imgur.com/VFKM2.gif) and then it is 
simply referred to when drawing characters. Textures can also be 
colorized, so the bitmap black & white is perfectly fine.
b) Maybe there are some ways to sharpen textures, but I am not very 
familiar with the topic.

> Antialiasing on lines is historically never been implemented on consumer
> cards (it was one of the 'differences' of the Quadros), but maybe now
> the situation is different. In fact the FireGL we used (still the IBM
> design, not the overpowered Radeon) had the 'line' primitives
> (evaluators included) completely done in HW, antialiasing and stuff. But
> only one texture stage :D

But for lines made from triangles it works 
http://oi58.tinypic.com/21n2s1j.jpg (yup, it is buggy, there is 
something wrong and currently I do not know how to fix it).

Regards,
Orson