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Reply From: |
xetaichohangpq |
I’ve written a sprite shader that rotates a sprite to face the camera along the Y-axis. The rotation itself is perfectly functional, but something strange happens when the sprite is viewed from certain specific angles.
At angles where the camera’s Y rotation differs from that of the sprite’s GameObject, nothing strange happens:
BillboardShader1.png
…But when they have matching Y rotations, (in this case, both zero) the sprite vanishes at certain values of the camera’s X rotation:
BillboardShader2.png
Again, the vanishing only seems to happen (from what I can tell) when their Y rotations match, as you can see here:
BillboardShader3.png
The scale of the sprite’s Transform also plays a part in what camera angles make it vanish. I’ve gotten the sprite to disappear a few times by just fiddling with its Z scale.
I’m really puzzled as to what’s causing this. I can only assume it has something to do with how my shader does the rotating, but I can’t figure out what.
Shader Code:
Code (CSharp):
Shader “Sprites/Billboard Y Only”
{
Properties
{
[PerRendererData] _MainTex (“Sprite Texture”, 2D) = “white” {}
_Color (“Tint”, Color) = (1,1,1,1)
_ScaleX (“Scale X”, Float) = 1.0
_ScaleY (“Scale Y”, Float) = 1.0
[MaterialToggle] PixelSnap (“Pixel snap”, Float) = 0
}
SubShader
{
Tags
{
"Queue"="Transparent"
"IgnoreProjector"="True"
"RenderType"="Transparent"
"PreviewType"="Plane"
"CanUseSpriteAtlas"="True"
"DisableBatching"="True"
}
Cull Off
Lighting Off
ZWrite Off
Blend One OneMinusSrcAlpha
Pass
{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma multi_compile _ PIXELSNAP_ON
#include "UnityCG.cginc"
struct appdata_t
{
float4 vertex : POSITION;
float4 color : COLOR;
float2 texcoord : TEXCOORD0;
};
struct v2f
{
float4 vertex : SV_POSITION;
fixed4 color : COLOR;
float2 texcoord : TEXCOORD0;
};
float4 RotateAroundYInDegrees (float4 vertex, float degrees)
{
float alpha = degrees * UNITY_PI / 180.0;
float sina, cosa;
sincos(alpha, sina, cosa);
float2x2 m = float2x2(cosa, -sina, sina, cosa);
return float4(mul(m, vertex.xz), vertex.yw).xzyw;
}
float4 RotateAroundYInRadians (float4 vertex, float radians)
{
float sina, cosa;
sincos(radians, sina, cosa);
float2x2 m = float2x2(cosa, -sina, sina, cosa);
return float4(mul(m, vertex.xz), vertex.yw).xzyw;
}
fixed4 _Color;
float _ScaleX;
float _ScaleY;
v2f vert(appdata_t IN)
{
v2f OUT;
IN.vertex *= float4(_ScaleX, _ScaleY, 1.0, 1.0); // Scale X and Y
float3 camDir = mul((float3x3)unity_CameraToWorld, float3(0,0,-1)); // Camera direction
camDir = mul((float3x3)unity_WorldToObject, camDir); // Put it in Object space (So object rotation won't affect it)
camDir.y = 0.0; // Discard Y axis to make it horizontal
float angle = acos(dot(normalize(camDir), normalize(float3(0.0, 0.0, -1.0)))); // Angle between horizontal camera direction and object forward
if (sign(camDir.x) < 0.0) { angle *= -1; } // Check if the angle should be negative
OUT.vertex = UnityObjectToClipPos(RotateAroundYInRadians (IN.vertex, angle)); // Calculate rotated vertex position (And put it in Clip space)
OUT.texcoord = IN.texcoord;
OUT.color = IN.color * _Color;
#ifdef PIXELSNAP_ON
OUT.vertex = UnityPixelSnap (OUT.vertex);
#endif
return OUT;
}
sampler2D _MainTex;
sampler2D _AlphaTex;
float _AlphaSplitEnabled;
fixed4 SampleSpriteTexture (float2 uv)
{
fixed4 color = tex2D (_MainTex, uv);
#if UNITY_TEXTURE_ALPHASPLIT_ALLOWED
if (_AlphaSplitEnabled)
color.a = tex2D (_AlphaTex, uv).r;
#endif //UNITY_TEXTURE_ALPHASPLIT_ALLOWED
return color;
}
sampler2D _CameraDepthNormalsTexture;
fixed4 frag(v2f IN) : SV_Target
{
fixed4 c = SampleSpriteTexture (IN.texcoord) * IN.color;
c.rgb *= c.a;
return c;
}
ENDCG
}
}
}
Source: xetaichohang
