[osg-users] [HELP] Properly using osg::VertexAttribDivisor for basic geometry instancing

ppsychrite at cock.li ppsychrite at cock.li
Wed Aug 1 05:16:50 PDT 2018

hello sorry if i did this wrong but i dont know how to use mailing lists

so ive been trying to do modern glsl/opengl 3.3+ with osg::Geometry and 
osg::Stateset and it's been working OK for basic triangle except for 
implementing instanced array data
am I doing it the wrong way? here's the .cpp code for it and for me it 
seems well enough and fine, position and color works fine

	osg::Vec3 coords[] = {
		{ -0.05f,0.05f,0.f },
		{ 0.05f,-0.05f,0.f },
		{ 0.05f,0.05f,1.f }
	osg::Vec3 colors[] = {

	osg::Vec2 instancetranslations[] = {
		{ 0.0f, 0.0f },
		{ 0.1f, 0.0f },
		{ 0.2f, 0.0f }

	osg::Vec3Array *pos = new osg::Vec3Array(sizeof(coords) / 
sizeof(osg::Vec3), coords);
	osg::Vec3Array *color = new osg::Vec3Array(sizeof(colors) / 
sizeof(osg::Vec3), colors);
	osg::Vec2Array *translation = new 
osg::Vec2Array(sizeof(instancetranslations) / sizeof(osg::Vec2), 

	osg::Geometry *vao = new osg::Geometry();

	vao->setVertexAttribArray(0, pos, osg::Array::BIND_PER_VERTEX);
	vao->setVertexAttribArray(1, color, osg::Array::BIND_PER_VERTEX);
	vao->setVertexAttribArray(2, translation);

	vao->addPrimitiveSet(new osg::DrawArrays(GL_TRIANGLES, 0, 3, 3)); //3 

	osg::ref_ptr<osg::Program> program = new osg::Program;


  	osg::StateSet *stateset = geom->getOrCreateStateSet();
	stateset->setAttribute(new osg::VertexAttribDivisor(2, 1)); //set 3rd 
array as per-instance

here's the vertex shader code for it:

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aColor;
layout (location = 2) in vec2 aTrans;

out vec3 color;

void main()
     color = aColor;
     gl_Position = vec4(aPos.x+ aTrans.x,aPos.y+ aTrans.y,aPos.z,1.0);

aTrans doesn't move the triangle at all, it's just one. I know it isn't 
the shaders fault because instead of adding aTrans to aPos I've done 
(gl_InstanceID * 0.1f) and it's worked perfectly, seeing 3 instanced 

what am i doing wrong/how could i get per-instanced array working?

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