View Full Version : 'stepped' contour plots ?
07-15-2005, 02:28 AM
I want to include 'stepped' contour plots like the one shown here
You can see there are distinct colour bands across the polygons as opposed to the 'default' linearly interpolated 'smooth' type of plot that you would get if you set a colour per vertex.
I have no idea how the stepped plots are done.
Any ideas on what to check out?
Thanks as always
07-15-2005, 04:13 AM
Per vertex glTexCoord1f(stress) with stress normalized to [0.0, 1.0] range and 1D texture mapping using GL_NEAREST filtering.
07-18-2005, 12:29 AM
Many thanks for taking the time to reply Relic
>>Per vertex glTexCoord1f(stress) with stress normalized to [0.0, 1.0] range and 1D texture mapping using GL_NEAREST filtering
I am working on texture mapping to normalized results at the moment (based on previous advice) but I assumed that this would produce an interpolated smooth plot across a polygon and not a steped plot?
So its the GL_NEAREST filtering that does the stepped display - yes?
07-18-2005, 01:20 AM
So its the GL_NEAREST filtering that does the
stepped display - yes?
exactly. GL_NEAREST means that the texture colors
are not interpolated.
one more thing: you may want to have a scale for
example from 500 to 1000. this means that a function
value of 0 would have a normalized texture
coordinate of -1.0; a value of 1500 would have
a texture coordinate of +2.0. you should therefore
use the texture parameter
glTexParameterf(GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
all texture coordinate values below 0.0 are
automatically set to 0.0, and all values above
1.0 are set to 1.0
all texture coordinate values below 0.0 are automatically set to 0.0, and all values above 1.0 are set to 1.0is that for GL_CLAMP_TO_EDGE or GL_CLAMP?
07-18-2005, 10:48 PM
it seems that with GL_CLAMP you get texture
coordinates from 0.0...1.0, with GL_CLAMP_TO_EDGE
the range depends on the texture size and is clamped
to 1/(2N)...1-1/(2N) with the texture having N
pixels. this means that for 32-pixel texture the
coordinates are between 1/64 and 1-1/64 (=63/64).
anyway, i tried both parameters and didn't see a
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