/// <summary>
/// Checks if the sprite pixel which resides at 'worldPos' is fully transparent.
/// </summary>
/// <remarks>
/// Works only when the Read/Write enabled flag is set inside the sprite texture
/// properties. Otherwise, it will always return false.
/// </remarks>
public static bool IsPixelFullyTransparent(this SpriteRenderer spriteRenderer, Vector3 worldPos)
{
// No sprite?
Sprite sprite = spriteRenderer.sprite;
if (sprite == null)
{
return(true);
}
// No texture?
Texture2D spriteTexture = sprite.texture;
if (spriteTexture == null)
{
return(true);
}
// We need to work in the sprite's model space so the first step is to transform
// the passed world position into a sprite local position.
Transform spriteTransform = spriteRenderer.transform;
Vector3 modelSpacePos = spriteTransform.InverseTransformPoint(worldPos);
// Project the model space position onto the sprite's plane. The sprite's plane is
// always the XY plane in its model space.
Plane xyPlane = new Plane(Vector3.forward, 0.0f);
Vector3 projectedPos = xyPlane.ProjectPoint(modelSpacePos);
// Calculate the sprite's model space AABB and check if this AABB contains the model
// space position. If it doesn't it means the suplied world position is outside the
// sprite's bounds/area.
AABB modelSpaceAABB = spriteRenderer.GetModelSpaceAABB();
modelSpaceAABB.Size = new Vector3(modelSpaceAABB.Size.x, modelSpaceAABB.Size.y, 1.0f);
if (!modelSpaceAABB.ContainsPoint(projectedPos))
{
return(true);
}
// Build a vector which goes from the bottom left of the sprite to the projected world
// position. This will help us calculate the coordinates of the pixel where the passed
// world point resides.
Vector3 bottomLeft = xyPlane.ProjectPoint(modelSpaceAABB.Min);
Vector3 fromTopLeftToPos = projectedPos - bottomLeft;
// Calculate the pixel coordinates of the passed world points
Vector2 pixelCoords = new Vector2(fromTopLeftToPos.x * sprite.pixelsPerUnit, fromTopLeftToPos.y * sprite.pixelsPerUnit);
pixelCoords += sprite.textureRectOffset;
// Try reading the sprite pixels and check the alpha value
try
{
float alpha = spriteTexture.GetPixel((int)(pixelCoords.x + 0.5f), (int)(pixelCoords.y + 0.5f)).a;
return(alpha <= 1e-3f);
}
catch (UnityException e)
{
// Ternary operator needed to avoid 'variable not used' warning
return(e != null ? false : false);
}
}
