2 replies to this topic

[codeman_nz]

Hi Everyone,

I put this on the graphics programming board but no one responded so I will put it on here.

Is it possible to have multiple calls to line strip using different vertices.

What I am doing is I have a loop with a bezier curve. In the loop it calculates the bezier point and another point above and below the point and the goal is to draw three separate lines with each of those points. At the moment I just put them into three arrays and then call glVertexPointer and glDrawArrays but it looks too ugly.

Any ideas?

[wodinoneeye]

Not really sure why 3 seperate renders look 'bad' as they wont have the connecting lines/triangs of trying to stuff all the data into one render.
DO these lines touch and they get garbled looking (probably would call for an outline for the line trace width)

You could either build trilists (triangle lists) instead to have full control of the facets (cant be much harder than the data setup for tristrip - just more data to be built -- 3 points for every triangle making of the rectangles making up your line segments)

Or add color attribute to the vertex data and add a few dummy segments with the coloring turned off alpha 0 when you realign back to the start of the
next of the 3 line traces. Make a coupla dummy color off triangles with the last point defining a trace line and then several more at the startposition of the first point of the next trace then turn the color back on in the points and add the next traces data into the same vertext buffer.

[codeman_nz]

I should put sample code to show what I am doing:
Vertex parallelPointsUp[101];
Vertex points[101];
Vertex parallelPointsDown[101];

for (int l = 0; l <= 100; l++)
{
calculate a bezier point and then a point on either side of it
}

glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, parallelPointsUp);
glDrawArrays(GL_LINE_STRIP, 0, 100);

glVertexPointer(3, GL_FLOAT, 0, parallelPointsDown);
glDrawArrays(GL_LINE_STRIP, 0, 100);

glVertexPointer(3, GL_FLOAT, 0, points);
glDrawArrays(GL_LINE_STRIP, 0, 100);

glDisableClientState(GL_VERTEX_ARRAY);

I just don't like have three arrays of 100 points. Any idea how too make it look better?