public override bool OnPaint(Terrain terrain, IOnPaint editContext)
{
BrushTransform brushXform = TerrainPaintUtility.CalculateBrushTransform(terrain, editContext.uv, editContext.brushSize, 0.0f);
PaintContext paintContext = TerrainPaintUtility.BeginPaintSurfaceMask(terrain, brushXform.GetBrushXYBounds());
Material mat = TerrainPaintUtility.GetBuiltinPaintMaterial();
float brushStrength = Event.current.shift ? editContext.brushStrength : -editContext.brushStrength;
Vector4 brushParams = new Vector4(brushStrength, 0.0f, 0.0f, 0.0f);
mat.SetTexture("_BrushTex", editContext.brushTexture);
mat.SetVector("_BrushParams", brushParams);
TerrainPaintUtility.SetupTerrainToolMaterialProperties(paintContext, brushXform, mat);
Graphics.Blit(paintContext.sourceRenderTexture, paintContext.destinationRenderTexture, mat, (int)TerrainPaintUtility.BuiltinPaintMaterialPasses.PaintSurfaceMask);
TerrainPaintUtility.EndPaintSurfaceMask(paintContext, "Terrain Paint - Paint Surface Mask");
return(true);
}