Merge pull request #879 from Tom94/fix-triangle-smoothness

Fix triangle smoothness and optimize further

osu.Game/Graphics/Backgrounds/Triangles.cs

@@ -23,6 +23,13 @@ namespace osu.Game.Graphics.Backgrounds
     public class Triangles : Drawable
     {
         private const float triangle_size = 100;
+        private const float base_velocity = 50;
+
+        /// <summary>
+        /// How many screen-space pixels are smoothed over.
+        /// Same behavior as Sprite's EdgeSmoothness.
+        /// </summary>
+        private const float edge_smoothness = 1;
 
         public override bool HandleInput => false;
 
@@ -103,31 +110,34 @@ namespace osu.Game.Graphics.Backgrounds
 
             Invalidate(Invalidation.DrawNode, shallPropagate: false);
 
-            for (int i = 0; i < parts.Count; i++)
+            if (CreateNewTriangles)
-            {
+                addTriangles(false);
-                TriangleParticle newParticle = parts[i];
 
             float adjustedAlpha = HideAlphaDiscrepancies ?
                 // Cubically scale alpha to make it drop off more sharply.
                 (float)Math.Pow(DrawInfo.Colour.AverageColour.Linear.A, 3) :
                 1;
 
+            float elapsedSeconds = (float)Time.Elapsed / 1000;
+            // Since position is relative, the velocity needs to scale inversely with DrawHeight.
+            // Since we will later multiply by the scale of individual triangles we normalize by
+            // dividing by triangleScale.
+            float movedDistance = -elapsedSeconds * Velocity * base_velocity / (DrawHeight * triangleScale);
 
-                newParticle.Position += new Vector2(0, -(parts[i].Scale * (50 / DrawHeight)) / triangleScale * Velocity) * ((float)Time.Elapsed / 950);
+            for (int i = 0; i < parts.Count; i++)
+            {
+                TriangleParticle newParticle = parts[i];
+
+                // Scale moved distance by the size of the triangle. Smaller triangles should move more slowly.
+                newParticle.Position.Y += parts[i].Scale * movedDistance;
                 newParticle.Colour.A = adjustedAlpha;
 
                 parts[i] = newParticle;
 
-                if (!CreateNewTriangles)
-                    continue;
-
                 float bottomPos = parts[i].Position.Y + triangle_size * parts[i].Scale * 0.866f / DrawHeight;
-
                 if (bottomPos < 0)
                     parts.RemoveAt(i);
             }
-
-            addTriangles(false);
         }
 
         private void addTriangles(bool randomY)
@@ -211,20 +221,28 @@ namespace osu.Game.Graphics.Backgrounds
                 Shader.Bind();
                 Texture.TextureGL.Bind();
 
+                Vector2 localInflationAmount = edge_smoothness * DrawInfo.MatrixInverse.ExtractScale().Xy;
+
                 foreach (TriangleParticle particle in Parts)
                 {
-                    var offset = new Vector2(particle.Scale * 0.5f, particle.Scale * 0.866f);
+                    var offset = triangle_size * new Vector2(particle.Scale * 0.5f, particle.Scale * 0.866f);
+                    var size = new Vector2(2 * offset.X, offset.Y);
 
                     var triangle = new Triangle(
                         particle.Position * Size * DrawInfo.Matrix,
-                        (particle.Position * Size + offset * triangle_size) * DrawInfo.Matrix,
+                        (particle.Position * Size + offset) * DrawInfo.Matrix,
-                        (particle.Position * Size + new Vector2(-offset.X, offset.Y) * triangle_size) * DrawInfo.Matrix
+                        (particle.Position * Size + new Vector2(-offset.X, offset.Y)) * DrawInfo.Matrix
                     );
 
                     ColourInfo colourInfo = DrawInfo.Colour;
                     colourInfo.ApplyChild(particle.Colour);
 
-                    Texture.DrawTriangle(triangle, colourInfo, null, Shared.VertexBatch.Add);
+                    Texture.DrawTriangle(
+                        triangle,
+                        colourInfo,
+                        null,
+                        Shared.VertexBatch.Add,
+                        Vector2.Divide(localInflationAmount, size));
                 }
 
                 Shader.Unbind();