Transformation matrix with surface shader


I’m writing a minimap with fog of war, focus, rotation and scaling features. Now I’ve hit a snag with the rotation part; somehow, it insists on rotating at the texture corner.

I’m using a matrix thusly:

 void UpdateMatrix()
    		if(target != null)
    			// get UV coordinates plus offset
    			posV = target.transform.position - world.transform.position;
    			posV.x = (posV.x/worldSize.x);
    			posV.z = (posV.z/worldSize.y);
    			posV.y = posV.z; // transform to XZ axis
    			posV.z = 0; 
    				// update the zoom level
    				scaV = new Vector3(zoom,zoom,zoom);
    				// restore the zoom level
    				scaV = new Vector3(1f,1f,1f);
    				// rotation on Y axis is remapped to texture's Z axis
    				rotQ = Quaternion.Euler(0,0,target.transform.eulerAngles.y);
    				rotQ = Quaternion.identity; // restore rotation
    			// no target, fixed view settings - restore position, no rotation, original scale
    			posV = new Vector3(0.5f,0.5f,0);
    			rotQ = Quaternion.identity;
    			scaV = new Vector3(1f,1f,1f);
    		matrix = Matrix4x4.TRS(posV,rotQ,scaV);

And the shader part:

SubShader {
		LOD 100
			"Queue" = "Transparent"
		Cull Off
		Lighting Off
		#pragma surface surf Lambert alpha
		struct Input
			float2 uv_MainTex;
		float _Zoom;
		float4x4 _Matrix;
		half4 _ActiveColor;
		half4 _ExploredColor;
		half4 _UnexploredColor;
		sampler2D _MainTex;
		sampler2D _FoWMask;
		sampler2D _CutoutMask;
		void surf (Input IN, inout SurfaceOutput o)
			half4 basec = tex2D(_MainTex, mul(_Matrix, float4(IN.uv_MainTex, 0, 1.0)).xy); // base
			half4 fowc = tex2D(_FoWMask, mul(_Matrix, float4(IN.uv_MainTex, 0, 1.0)).xy);  // FoW
			half4 finalc = lerp(lerp(_UnexploredColor,_ExploredColor,fowc.g),_ActiveColor,fowc.r); // FoW adjusted color
			o.Emission = basec.rgb * finalc.rgb;
			o.Alpha = basec.a * tex2D(_CutoutMask, IN.uv_MainTex).a;

Note that the world uses XZ plane reference. No matter what I do, I can’t seem to get the shader to rotate the textures at the given pivot. Why is that? What am I doing wrong here? I am at the end of my wits.

And yes, I am a beginner, so please do go easy on me!

Thanks for your time.

Welp, solved on my own after sleeping it through. The issue was that it rotated the texture around offset from the desired position.

The solution: use two matrices - one to translate,rotate around the desired pivot and scale up. And the other to translate to center of the texture AFTER the rotation and scaling have been done.

	Matrix4x4 m0 = Matrix4x4.TRS(posV,rotQ,scaV); // translate to target position, rotate and scale
	Matrix4x4 m1 = Matrix4x4.TRS(new Vector3(-0.5f,-0.5f,0),Quaternion.identity,; // translate to the center
	matrix = m0*m1;