Size vertex buffer ignored in a Mode.Points mesh?

CWI · January 19, 2021, 1:16pm

Hello,

I am rendering a point cloud using vertex buffers in a mesh.

Mesh m = new Mesh();
m.setMode(Mode.Points);
m.setBuffer(VertexBuffer.Type.Position, 3, pointCoordinates3d);
m.setBuffer(VertexBuffer.Type.Color, 4, colorsRGBA);
m.setBuffer(VertexBuffer.Type.Size, 1, sizes);

pointCoordinate3d contains the coordinates of the points, colorsRGBA the colors of points, and sizes the sizes of the points. I would expect that higher values in sizes would lead to the points being rendered larger, which isn’t the case.

Now a few questions:

Is what I described what the size vertex buffer is supposed to do?
If no, what is it supposed to do?
If yes, what could be the cause of the size buffer apparently being ignored?

Thank you and best regards
Christian

The_Leo · January 19, 2021, 1:39pm

Not really.
Each vertex buffer simply links the data, so that it is available to the shader.

It’s up to the shader to use the data in the way you’d like. As far as I know, the jME default Unshaded material’s vertex shader does not read and use attribute inSize.

Eg.: your vertex shader could contain the following to receive the input from vertex buffer size and set it to gl_PointSize.

...
attribute float inSize;
...
void main() {
	gl_PointSize = inSize;
	...

Depending on your requirements, gl_PointSize is limited on some hardware. An alternative to draw points or varying sizes is to use quads - billboards with instancing.

pspeed · January 19, 2021, 1:45pm

Or point sprites.

JME’s point could shader will use the size buffer as I recall. Particle.j3md I think.

CWI · January 19, 2021, 3:24pm

The particle shader seems to ignore sizes, that’s the one I am using.

pspeed · January 19, 2021, 3:28pm

Yes, for gl_points, size means nothing. You have to set the size at the material level once and even then it might not be supported.

Point SPRITES, as in images for the points, point images, point sprites, texture atlas with a sprite per point… should use size.

Note how the only size related code depends on point sprites:

github.com

jMonkeyEngine/jmonkeyengine/blob/master/jme3-core/src/main/resources/Common/MatDefs/Misc/Particle.vert#L33


void main(){
    vec4 pos = vec4(inPosition, 1.0);

    gl_Position = g_WorldViewProjectionMatrix * pos;
    color = inColor;

    #ifdef USE_TEXTURE
        texCoord = inTexCoord;
    #endif

    #ifdef POINT_SPRITE
        vec4 worldPos = g_WorldMatrix * pos;
        float d = distance(g_CameraPosition.xyz, worldPos.xyz);
        float size = (inSize * SIZE_MULTIPLIER * m_Quadratic) / d;
        gl_PointSize = max(1.0, size);

        //vec4 worldViewPos = g_WorldViewMatrix * pos;
        //gl_PointSize = (inSize * SIZE_MULTIPLIER * m_Quadratic)*100.0 / worldViewPos.z;

        color.a *= min(size, 1.0);
    #endif

…you will be disappointed with OpenGL point sizes for OpenGL points.