Implement pixel shader for rendering 8-bit effect -like style.

osu.Framework.Font.Tests/Visual/Shaders/CustomizedShaderTestScene.cs

@@ -6,6 +6,7 @@
 using osu.Framework.Extensions.Color4Extensions;
 using osu.Framework.Font.Tests.Helper;
 using osu.Framework.Graphics.Shaders;
+using osuTK;
 
 namespace osu.Framework.Font.Tests.Visual.Shaders
 {
@@ -72,5 +73,22 @@ public void TestRainbowShader(string uv, float speed, float saturation, float br
                 };
             });
         }
+
+        [TestCase(5, 5)]
+        [TestCase(5, 20)]
+        [TestCase(20, 20)]
+        public void TestPixelShader(float x, float y)
+        {
+            AddStep("Apply shader", () =>
+            {
+                ShaderContainer.Shaders = new[]
+                {
+                    GetShaderByType<PixelShader>().With(s =>
+                    {
+                        s.Size = new Vector2(x, y);
+                    })
+                };
+            });
+        }
     }
 }

osu.Framework.Font/Extensions/ShaderManagerExtensions.cs

@@ -17,6 +17,7 @@ public static T LocalCustomizedShader<T>(this ShaderManager shaderManager) where
                 Type _ when type == typeof(OutlineShader) => new OutlineShader(shaderManager.Load(VertexShaderDescriptor.TEXTURE_2, OutlineShader.SHADER_NAME)) as T,
                 Type _ when type == typeof(RainbowShader) => new RainbowShader(shaderManager.Load(VertexShaderDescriptor.TEXTURE_2, RainbowShader.SHADER_NAME)) as T,
                 Type _ when type == typeof(ShadowShader) => new ShadowShader(shaderManager.Load(VertexShaderDescriptor.TEXTURE_2, ShadowShader.SHADER_NAME)) as T,
+                Type _ when type == typeof(PixelShader) => new PixelShader(shaderManager.Load(VertexShaderDescriptor.TEXTURE_2, PixelShader.SHADER_NAME)) as T,
                 _ => throw new NotImplementedException()
             };
         }

osu.Framework.Font/Graphics/Shaders/PixelShader.cs

@@ -0,0 +1,29 @@
+// Copyright (c) andy840119 <[email protected]>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Graphics.OpenGL.Buffers;
+using osuTK;
+
+namespace osu.Framework.Graphics.Shaders
+{
+    public class PixelShader : CustomizedShader
+    {
+        public const string SHADER_NAME = "Pixel";
+
+        public Vector2 Size { get; set; } = new Vector2(5);
+
+        public PixelShader(IShader originShader)
+            : base(originShader)
+        {
+        }
+
+        public override void ApplyValue(FrameBuffer current)
+        {
+            var size = Size;
+            GetUniform<Vector2>(@"g_Size").UpdateValue(ref size);
+
+            var textureSize = current.Size;
+            GetUniform<Vector2>(@"g_TexSize").UpdateValue(ref textureSize);
+        }
+    }
+}

osu.Framework.Font/Resources/Shaders/sh_Pixel.fs

@@ -0,0 +1,18 @@
+// see the demo: https://www.geeks3d.com/20101029/shader-library-pixelation-post-processing-effect-glsl/
+
+varying mediump vec2 v_TexCoord;
+
+uniform lowp sampler2D m_Sampler;
+
+uniform mediump vec2 g_TexSize;
+uniform mediump vec2 g_Size;
+
+void main(void) 
+{ 
+	vec2 separaorParts = g_TexSize / g_Size;
+	vec2 uv = v_TexCoord;
+	uv = uv * separaorParts;
+    uv = floor(uv);
+    uv = uv / separaorParts;
+    gl_FragColor = texture2D(m_Sampler, uv);
+}