OK I did it!
I followed this lovely tutorial. => WebGL 3D Perspective Correct Texture Mapping
All you have to do is divide the gl_Position by the w value.
varying vec2 _uv;
void main()
{
_uv = uv;
vec4 modelViewPosition = modelViewMatrix * vec4(position, 1.0);
gl_Position = projectionMatrix * modelViewPosition;
//this line makes all the difference
gl_Position /= gl_Position.w ;
}
I’m not super sure yet why this does the job…
EDIT: actually the tutorial explains why this is perfectly - lol i’m stupid. Good day everyone! 