Making a billboard shader in Unity

Question

I followed this guy's tutorial on making a billboard shader, and it works great, except if you are billboarding things that are tall, like a tree, it looks weird, to put it simply.

When the camera's horizontal rotation is zero, it looks fine, as you can see: the trees up close are models the ones far away are billboards

But when you rotate to look up or down, the tree billboards rotate with the camera, this is particularly apparent when the up close 3D trees are pointing the correct way but the billboards in the distance are not.

So I just need to know how to get it to rotate in the way I want but not in the way I don't want:

            float4 worldOrigin = mul(UNITY_MATRIX_M, float4(0, 0, 0, 1));
            float4 viewOrigin = float4(UnityObjectToViewPos(float3(0, 0, 0)), 1);
            float4 worldPos = mul(UNITY_MATRIX_M, v.vertex);


            float4 viewPos = worldPos - worldOrigin + viewOrigin; // the tutorial's way of doing it for billboarding

            //float4 viewPos = mul(UNITY_MATRIX_V, worldPos); // the normal way, basically turns it into an unlit shader


            float4 clipsPos = mul(UNITY_MATRIX_P, viewPos);
            o.vertex = clipsPos;

I've tried a million things, like seeing what it looks like when you multiply some of the vectors in the UNITY_MATRIX_V matrix by 0 or by another vector before using mul() on it. So is there anyway for them to behave when the camera rotates up and down as well as have them always face the player? Thank you, here is the full code just in case: thank you!

Shader "Billboard"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _Color("Color", Color) = (1,1,1,1)
    }
    SubShader
    {
        Tags { "RenderType"="Transparent" "Queue"="Transparent+500" }
        LOD 100

        Pass
        {
        
            ZTest Off
            Blend SrcAlpha OneMinusSrcAlpha
            Cull Off
        
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_instancing
            // make fog work
            #pragma multi_compile_fog

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
                float4 color : COLOR;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
                float4 color : COLOR0;
                UNITY_VERTEX_INPUT_INSTANCE_ID // necessary only if you want to access instanced properties in fragment Shader.
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;

            UNITY_INSTANCING_BUFFER_START(Props)
            UNITY_DEFINE_INSTANCED_PROP(float4, _Color)
            UNITY_INSTANCING_BUFFER_END(Props)


            v2f vert (appdata v)
            {
                v2f o;

                UNITY_SETUP_INSTANCE_ID(v);
                UNITY_TRANSFER_INSTANCE_ID(v, o); // necessary only if you want to access instanced properties in the fragment Shader.


                float4 worldOrigin = mul(UNITY_MATRIX_M, float4(0, 0, 0, 1));
                float4 viewOrigin = float4(UnityObjectToViewPos(float3(0, 0, 0)), 1);
                float4 worldPos = mul(UNITY_MATRIX_M, v.vertex);


                float4 viewPos = worldPos - worldOrigin + viewOrigin; // the tutorial's way of doing it for billboarding

                //float4 viewPos = mul(UNITY_MATRIX_V, worldPos); // the normal way, basically turns it into an unlit shader


                float4 clipsPos = mul(UNITY_MATRIX_P, viewPos);
                o.vertex = clipsPos;

                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                UNITY_TRANSFER_FOG(o,o.vertex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // sample the texture
                fixed4 col = UNITY_ACCESS_INSTANCED_PROP(Props, _Color) * tex2D(_MainTex, i.uv);

                // apply fog
                UNITY_APPLY_FOG(i.fogCoord, col);

                UNITY_SETUP_INSTANCE_ID(i); // necessary only if any instanced properties are going to be accessed in the fragment Shader.


                return col;

                //return col;
            }
            ENDCG
        }
    }
}

Answer 1

So obviously you just don't take out the camera rotation part of the matrix that the code above takes out, I just didn't know what the various parts of the matrix meant and through a long time of trial and error nothing seemed to make sense but this guy on Reddit explained everything perfectly and even wrote shader code which works. After adding his code my shader now looks like this:

Shader "Billboard"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _Color("Color", Color) = (1,1,1,1)
    }
    SubShader
    {
        Tags { "IGNOREPROJECTOR" = "true" "RenderType"="Transparent" "Queue"="Transparent+500" } //"LIGHTMODE"="FORWARDBASE" "QUEUE"="AlphaTest" "IGNOREPROJECTOR"="true" "SHADOWSUPPORT"="true" "RenderType"="TransparentCutout" "DisableBatching"="LodFading"
        LOD 100

        Pass
        {
        
            //ZTest Off
            Blend SrcAlpha OneMinusSrcAlpha
            Cull Off
        
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_instancing
            // make fog work
            #pragma multi_compile_fog

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
                float4 color : COLOR;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
                float4 color : COLOR0;
                UNITY_VERTEX_INPUT_INSTANCE_ID // necessary only if you want to access instanced properties in fragment Shader.
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;

            UNITY_INSTANCING_BUFFER_START(Props)
            UNITY_DEFINE_INSTANCED_PROP(float4, _Color)
            UNITY_INSTANCING_BUFFER_END(Props)


            v2f vert (appdata v)
            {
                v2f o;

                UNITY_SETUP_INSTANCE_ID(v);
                UNITY_TRANSFER_INSTANCE_ID(v, o); // necessary only if you want to access instanced properties in the fragment Shader.


                //copy them so we can change them (demonstration purpos only)
                float4x4 newViewMatrix = UNITY_MATRIX_V;

                //break out the axis
                float3 right = normalize(newViewMatrix._m00_m01_m02);
                float3 up = float3(0, 1, 0);
                float3 forward = normalize(newViewMatrix._m20_m21_m22);
                //get the rotation parts of the matrix
                float4x4 rotationMatrix = float4x4(
                    right, 0,
                    up, 0,
                    forward, 0,
                    0, 0, 0, 1);

                //the inverse of a rotation matrix happens to always be the transpose
                float4x4 rotationMatrixInverse = transpose(rotationMatrix);

                //apply the rotationMatrixInverse, model, view and projection matrix
                float4 pos = v.vertex;
                pos = mul(rotationMatrixInverse, pos);
                pos = mul(UNITY_MATRIX_M, pos);
                pos = mul(newViewMatrix, pos);
                pos = mul(UNITY_MATRIX_P, pos);
                o.vertex = pos;

                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                UNITY_TRANSFER_FOG(o,o.vertex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // sample the texture
                fixed4 col = UNITY_ACCESS_INSTANCED_PROP(Props, _Color) * tex2D(_MainTex, i.uv);
                // apply fog
                UNITY_APPLY_FOG(i.fogCoord, col);
                UNITY_SETUP_INSTANCE_ID(i); // necessary only if any instanced properties are going to be accessed in the fragment Shader.
                return col;
            }
            ENDCG
        }
    }
}