[Opensg-users] Billboard particle shader

[Victor Haefner]

Hi all,

the gl_ProjectionMatrix allows me to compute the up and right vector in
view coordinates.
vec4 right = gl_ProjectionMatrix*vec4(1,0,0);
vec4 up = gl_ProjectionMatrix*vec4(0,1,0);
I can use those vectors to create a nice quad in the geometry shader.

The problem is when using head tracking (OSGProjectionCameraDecorator).
The orientation of the head messes with the gl_ProjectionMatrix, and thus
with the shape of my quad.

I essentially just need the aspect ratio of the viewport in my shader.
Passing it as a variable is not possible (I think?) because I have a
cluster environment, multiple viewports, with different aspect ratios...

thanks for reading!
best regards,
Victor

[Carsten Neumann]

Hello Victor,

Post by Victor Haefner
the gl_ProjectionMatrix allows me to compute the up and right vector in
view coordinates.
vec4 right = gl_ProjectionMatrix*vec4(1,0,0);
vec4 up = gl_ProjectionMatrix*vec4(0,1,0);
I can use those vectors to create a nice quad in the geometry shader.
The problem is when using head tracking (OSGProjectionCameraDecorator).
The orientation of the head messes with the gl_ProjectionMatrix, and
thus with the shape of my quad.
I essentially just need the aspect ratio of the viewport in my shader.
Passing it as a variable is not possible (I think?) because I have a
cluster environment, multiple viewports, with different aspect ratios...

you can use one of the 'magic' OpenSG variables:
uniform vec2 OSGViewportSize;

see Source/State/Shader/Variables/OSGShaderVariableOSG.{h,cpp} and
ShaderProgram::addOSGVariable()

Cheers,
Carsten

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[Victor Haefner]

Hello Carsten,

Thanks a lot! this is exactly what I needed!! :)

best regards,
Victor

Post by Carsten Neumann
Hello Victor,

Post by Victor Haefner
the gl_ProjectionMatrix allows me to compute the up and right vector in
view coordinates.
vec4 right = gl_ProjectionMatrix*vec4(1,0,0);
vec4 up = gl_ProjectionMatrix*vec4(0,1,0);
I can use those vectors to create a nice quad in the geometry shader.
The problem is when using head tracking (OSGProjectionCameraDecorator).
The orientation of the head messes with the gl_ProjectionMatrix, and
thus with the shape of my quad.
I essentially just need the aspect ratio of the viewport in my shader.
Passing it as a variable is not possible (I think?) because I have a
cluster environment, multiple viewports, with different aspect ratios...

uniform vec2 OSGViewportSize;
see Source/State/Shader/Variables/OSGShaderVariableOSG.{h,cpp} and
ShaderProgram::addOSGVariable()
Cheers,
Carsten
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