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ic0de

Weird point sprite perspective

4 posts in this topic

So I have this problem where my point sprites are not becoming smaller as the get farther from the camera but rather larger. I tried GL_POINT_DISTANCE_ATTENUATION but it didn't seem to have any affect. I also wrote a shader to scale the point sprites based on there distance:

[CODE]
gl_PointSize = scr_h / distance(-(gl_ModelViewMatrix * gl_Vertex), gl_Vertex);
[/CODE]

This works but doesn't stop the sprites from getting bigger, what happens is that the sprite gets smaller with distance but only starting at a certain point before that the are growing forming a sort of "bulge" in the middle of a row of sprites. Any idea where this scaling upward is coming from, is there something that I can disable? I certainly didn't enable anything except this:

[CODE]
glEnable(GL_POINT_SPRITE);
glTexEnvi(GL_POINT_SPRITE, GL_COORD_REPLACE, GL_TRUE);
glEnable(GL_VERTEX_PROGRAM_POINT_SIZE);
[/CODE]
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[quote name='ic0de' timestamp='1348186098' post='4982200']
gl_PointSize = scr_h / distance(-(gl_ModelViewMatrix * gl_Vertex), gl_Vertex);
[/quote]
What are you doing here ? You take the distance between a point in [i]object space [/i]and [i]camera space[/i], what is your object space for point sprites ? When you have a transformed point in camera space, the camera position is (0,0,0), therefore you just need either this for linear depth

[CODE]
// assumption: -z points into the screen
gl_PointSize = scr_h / -(gl_ModelViewMatrix * gl_Vertex).z;
[/CODE]

or this for radial depth
[CODE]
vec3 pointInCS = (gl_ModelViewMatrix * gl_Vertex);
gl_PointSize = scr_h / sqrt(dot(pointInCS,pointInCS));
[/CODE]
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[quote name='Ashaman73' timestamp='1348204862' post='4982242']
[quote name='ic0de' timestamp='1348186098' post='4982200']
gl_PointSize = scr_h / distance(-(gl_ModelViewMatrix * gl_Vertex), gl_Vertex);
[/quote]
What are you doing here ? You take the distance between a point in [i]object space [/i]and [i]camera space[/i], what is your object space for point sprites ? When you have a transformed point in camera space, the camera position is (0,0,0).
[/quote]

True, I modified my code based on your suggestion for radial depth but the problem seems to be coming from somewhere outside the shader. Is there a way I can make sure that gl_PointSize is only affected by the shader and nothing else? Edited by ic0de
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Issue seems to be with the NVIDIA driver, I ported the same game from windows to Linux and the problem just went away, no code changes all cross platform libs. I was wondering if anyone knew any workarounds so that the windows one can work?
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[quote name='ic0de' timestamp='1348519331' post='4983353']
I was wondering if anyone knew any workarounds so that the windows one can work?
[/quote]
Don't use point sprites [img]http://public.gamedev.net//public/style_emoticons/default/tongue.png[/img] To be honest, point sprites in OGL have a long history of issues, either on ATI or on NVidia videocards. I would use geometry shaders instead and quads as fallback for older videocards.
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