How can I transform a primitive using only GL and matrix multiplication (no GameObject)?

Questions & Answers
1

Hello, I’ve been creating simple primitives in Unity using GL (without Gizmos since it needs to be more versatile). The initial drawing of the classes I have implemented (like “line” and “circle”) are drawing fine. Here’s an example:

class LineAnnotation : Annotation
    {
        Vector3[] vertices { get; set; }
        Color LineColor = new Color(0,0,0,1);
        
        public LineAnnotation(Vector3 start, Vector3 end)
        {
		    vertices = new Vector3[2] {
			    start,
				end
			};
			if(material == null) { 
        		CreateMaterial();
    		} 
        }

        public override void Draw()
        {
			GL.PushMatrix();
			if (material != null) {
				material.SetPass(0);
			}
			GL.Begin(GL.LINES);
			GL.Color(new Color(0,0,0));
			GL.Vertex(vertices[0]);
			GL.Vertex(vertices[1]);
			GL.End();
			GL.PopMatrix();
			
        }
	
		

    }

However, I also have “Transform” classes which need to translate, rotate, or scale a given primitive. The problem is that the transforms are not happening. The primitives get drawn in their initial positions, even when they’re inside of a Transform object that is storing the vector translation. See my code below:

This is the draw method for my translation class, and below that is the one for scaling:

    public override void Draw() // The translation one.
    {
        GL.PushMatrix(); // Save Matrix
        GL.modelview.SetTRS(Translation,Quaternion.identity, Vector3.one); // Change Translation, but leave the other parts of the matrix alone.
        DrawChildren();  // Draws the primitives it was passed
        GL.PopMatrix();  // Restore Matrix
}
public override void Draw() //This is the scaling one. 
    {
        GL.PushMatrix(); // Save Matrix
        GL.modelview.SetTRS(Vector3.zero,Quaternion.identity, new Vector3(Scale, Scale, Scale)); // Change Scale part of modelview, but leave the other parts of the matrix alone.
        DrawChildren();  // Draws the primitives it was passed
        GL.PopMatrix();  // Restore Matrix
    }

Does anyone have any ideas about why this is happening? I feel like there’s a pretty easy fix to it that I’m missing, but it can’t be that hard to transform the modelview matrix so that I can transform whatever child primitive is being drawn, and then pop back out so I can get on with drawing other primitives. Any thoughts or advice is welcome.

2

var matrix = Matrix4x4.TRS(…);

GL.PushMatrix();
GL.MultMatrix(matrix);

//Draw

GL.PopMatrix();

This worked for me.