修复导出过程中的PMA问题

SpineViewer/Exporter/ExportArgs.cs

@@ -72,7 +72,27 @@ namespace SpineViewer.Exporter
         [Editor(typeof(SFMLColorEditor), typeof(UITypeEditor))]
         [TypeConverter(typeof(SFMLColorConverter))]
         [Category("[0] 导出"), DisplayName("背景颜色"), Description("要使用的背景色, 格式为 #RRGGBBAA")]
-        public SFML.Graphics.Color BackgroundColor { get; set; } = SFML.Graphics.Color.Transparent;
+        public SFML.Graphics.Color BackgroundColor 
+        {
+            get => backgroundColor;
+            set
+            {
+                backgroundColor = value;
+                var bcPma = value;
+                var a = bcPma.A / 255f;
+                bcPma.R = (byte)(bcPma.R * a);
+                bcPma.G = (byte)(bcPma.G * a);
+                bcPma.B = (byte)(bcPma.B * a);
+                BackgroundColorPma = bcPma;
+            }
+        }
+        private SFML.Graphics.Color backgroundColor = SFML.Graphics.Color.Transparent;
+
+        /// <summary>
+        /// 预乘后的背景颜色
+        /// </summary>
+        [Browsable(false)]
+        public SFML.Graphics.Color BackgroundColorPma { get; private set; } = SFML.Graphics.Color.Transparent;
 
         /// <summary>
         /// 检查参数是否合法并规范化参数值, 否则返回用户错误原因

SpineViewer/Exporter/Exporter.cs

@@ -1,5 +1,4 @@
 using NLog;
-using SpineViewer.Spine;
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
@@ -52,28 +51,55 @@ namespace SpineViewer.Exporter
         /// <summary>
         /// 获取单个模型的单帧画面
         /// </summary>
-        protected SFMLImageVideoFrame GetFrame(Spine.Spine spine)
+        protected SFMLImageVideoFrame GetFrame(Spine.Spine spine) => GetFrame([spine]);
-        {
-            // tex 必须临时创建, 随用随取, 防止出现跨线程的情况
-            using var tex = GetRenderTexture();
-            tex.Clear(ExportArgs.BackgroundColor);
-            tex.Draw(spine);
-            tex.Display();
-            return new(tex.Texture.CopyToImage());
-        }
 
         /// <summary>
         /// 获取模型列表的单帧画面
         /// </summary>
         protected SFMLImageVideoFrame GetFrame(Spine.Spine[] spinesToRender)
         {
-            // tex 必须临时创建, 随用随取, 防止出现跨线程的情况
+            // RenderTexture 必须临时创建, 随用随取, 防止出现跨线程的情况
+            using var texPma = GetRenderTexture();
+
+            // 先将预乘结果准确绘制出来, 注意背景色也应当是预乘的
+            texPma.Clear(ExportArgs.BackgroundColorPma);
+            foreach (var spine in spinesToRender) texPma.Draw(spine);
+            texPma.Display();
+
+            // 背景色透明度不为 1 时需要处理反预乘, 否则直接就是结果
+            if (ExportArgs.BackgroundColor.A < 255)
+            {
+                // 从预乘结果构造渲染对象, 并正确设置变换
+                using var view = texPma.GetView();
+                using var img = texPma.Texture.CopyToImage();
+                using var texSprite = new SFML.Graphics.Texture(img);
+                using var sp = new SFML.Graphics.Sprite(texSprite)
+                {
+                    Origin = new(texPma.Size.X / 2f, texPma.Size.Y / 2f),
+                    Position = new(view.Center.X, view.Center.Y),
+                    Scale = new(view.Size.X / texPma.Size.X, view.Size.Y / texPma.Size.Y),
+                    Rotation = view.Rotation
+                };
+
+                // 混合模式用直接覆盖的方式, 保证得到的图像区域是反预乘的颜色和透明度, 同时使用反预乘着色器
+                var st = SFML.Graphics.RenderStates.Default;
+                st.BlendMode = new(SFML.Graphics.BlendMode.Factor.One, SFML.Graphics.BlendMode.Factor.Zero); // 用源的颜色和透明度直接覆盖
+                st.Shader = Shader.InversePma;
+
+                // 在最终结果上二次渲染非预乘画面
                 using var tex = GetRenderTexture();
+
+                // 将非预乘结果覆盖式绘制在目标对象上, 注意背景色应该用非预乘的
                 tex.Clear(ExportArgs.BackgroundColor);
-            foreach (var spine in spinesToRender) tex.Draw(spine);
+                tex.Draw(sp, st);
                 tex.Display();
                 return new(tex.Texture.CopyToImage());
             }
+            else
+            {
+                return new(texPma.Texture.CopyToImage());
+            }
+        }
 
         /// <summary>
         /// 每个模型在同一个画面进行导出

SpineViewer/Exporter/Implementations/ExportArgs/GifExportArgs.cs

@@ -16,9 +16,6 @@ namespace SpineViewer.Exporter.Implementations.ExportArgs
     {
         public GifExportArgs(Size resolution, SFML.Graphics.View view, bool renderSelectedOnly) : base(resolution, view, renderSelectedOnly) 
         {
-            // 给一个纯白的背景
-            BackgroundColor = new(255, 255, 255, 0);
-
             // GIF 的帧率不能太高, 超过 50 帧反而会变慢
             FPS = 12;
         }

SpineViewer/Exporter/Implementations/ExportArgs/MkvExportArgs.cs

@@ -16,7 +16,7 @@ namespace SpineViewer.Exporter.Implementations.ExportArgs
     {
         public MkvExportArgs(Size resolution, SFML.Graphics.View view, bool renderSelectedOnly) : base(resolution, view, renderSelectedOnly)
         {
-            BackgroundColor = new(0, 255, 0, 0);
+            BackgroundColor = new(0, 255, 0);
         }
 
         public override string Format => "matroska";

SpineViewer/Exporter/Implementations/ExportArgs/MovExportArgs.cs

@@ -16,7 +16,7 @@ namespace SpineViewer.Exporter.Implementations.ExportArgs
     {
         public MovExportArgs(Size resolution, SFML.Graphics.View view, bool renderSelectedOnly) : base(resolution, view, renderSelectedOnly)
         {
-            BackgroundColor = new(0, 255, 0, 0);
+            BackgroundColor = new(0, 255, 0);
         }
 
         public override string Format => "mov";

SpineViewer/Exporter/Implementations/ExportArgs/Mp4ExportArgs.cs

@@ -16,7 +16,7 @@ namespace SpineViewer.Exporter.Implementations.ExportArgs
     {
         public Mp4ExportArgs(Size resolution, SFML.Graphics.View view, bool renderSelectedOnly) : base(resolution, view, renderSelectedOnly)
         {
-            BackgroundColor = new(0, 255, 0, 0);
+            BackgroundColor = new(0, 255, 0);
         }
 
         public override string Format => "mp4";

SpineViewer/MainForm.cs

@@ -28,7 +28,7 @@ namespace SpineViewer
             // 执行一些初始化工作
             try
             {
-                Spine.Shader.Init();
+                Shader.Init();
             }
             catch (Exception ex)
             {

SpineViewer/Shader.cs

@@ -4,39 +4,39 @@ using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 
-namespace SpineViewer.Spine
+namespace SpineViewer
 {
     public static class Shader
     {
         /// <summary>
         /// 用于非预乘纹理的 fragment shader, 乘上了插值后的透明度用于实现透明度变化(插值预乘), 并且输出预乘后的像素值
         /// </summary>
-        private const string FRAGMENT_VertexAlpha = (
+        private const string FRAGMENT_VertexAlpha = 
             "uniform sampler2D t;" +
             "void main() { vec4 p = texture(t, gl_TexCoord[0].xy);" +
             "p.rgb *= p.a * gl_Color.a;" +
             "gl_FragColor = gl_Color * p; }"
-        );
+        ;
 
         /// <summary>
         /// 用于预乘纹理的 fragment shader, 乘上了插值后的透明度用于实现透明度变化(插值预乘)
         /// </summary>
-        private const string FRAGMENT_VertexAlphaPma = (
+        private const string FRAGMENT_VertexAlphaPma = 
             "uniform sampler2D t;" +
             "void main() { vec4 p = texture(t, gl_TexCoord[0].xy);" +
             "p.rgb *= gl_Color.a;" +
             "gl_FragColor = gl_Color * p; }"
-        );
+        ;
 
         /// <summary>
         /// 预乘转非预乘 fragment shader
         /// </summary>
-        private const string FRAGMENT_PmaInv = (
+        private const string FRAGMENT_InvPma = 
             "uniform sampler2D t;" +
             "void main() { vec4 p = texture(t, gl_TexCoord[0].xy);" +
-            "p.rgb *= gl_Color.a;" +
+            "if (p.a > 0) p.rgb /= max(max(max(p.r, p.g), p.b), p.a);" +
-            "gl_FragColor = gl_Color * p; }"
+            "gl_FragColor = p; }"
-        );
+        ;
 
         /// <summary>
         /// 考虑了顶点透明度变化的着色器, 输入是非预乘纹理像素, 输出是预乘像素
@@ -48,6 +48,11 @@ namespace SpineViewer.Spine
         /// </summary>
         private static SFML.Graphics.Shader? VertexAlphaPma = null;
 
+        /// <summary>
+        /// 反预乘着色器, 用于得到正确透明度的非预乘画面
+        /// </summary>
+        public static SFML.Graphics.Shader? InversePma { get; private set; }
+
         /// <summary>
         /// 加载 Shader, 可能会存在异常导致着色器加载失败
         /// </summary>
@@ -56,14 +61,15 @@ namespace SpineViewer.Spine
         {
             VertexAlpha = SFML.Graphics.Shader.FromString(null, null, FRAGMENT_VertexAlpha);
             VertexAlphaPma = SFML.Graphics.Shader.FromString(null, null, FRAGMENT_VertexAlphaPma);
+            InversePma = SFML.Graphics.Shader.FromString(null, null, FRAGMENT_InvPma);
         }
 
         /// <summary>
-        /// 获取合适的着色器
+        /// 获取绘制 Spine 的着色器
         /// </summary>
         /// <param name="pma">纹理是否是预乘的</param>
         /// <param name="twoColor">是否是双色着色的(TODO)</param>
-        public static SFML.Graphics.Shader? GetShader(bool pma, bool twoColor = false)
+        public static SFML.Graphics.Shader? GetSpineShader(bool pma, bool twoColor = false)
         {
             if (pma)
                 return VertexAlphaPma;

SpineViewer/Spine/Implementations/Spine/Spine21.cs

@@ -261,7 +261,7 @@ namespace SpineViewer.Spine.Implementations.Spine
         {
             vertexArray.Clear();
             states.Texture = null;
-            states.Shader = Shader.GetShader(usePremultipliedAlpha);
+            states.Shader = Shader.GetSpineShader(usePremultipliedAlpha);
 
             // 要用 DrawOrder 而不是 Slots
             foreach (var slot in skeleton.DrawOrder)

SpineViewer/Spine/Implementations/Spine/Spine36.cs

@@ -220,7 +220,7 @@ namespace SpineViewer.Spine.Implementations.Spine
         {
             vertexArray.Clear();
             states.Texture = null;
-            states.Shader = Shader.GetShader(usePremultipliedAlpha);
+            states.Shader = Shader.GetSpineShader(usePremultipliedAlpha);
 
             // 要用 DrawOrder 而不是 Slots
             foreach (var slot in skeleton.DrawOrder)

SpineViewer/Spine/Implementations/Spine/Spine37.cs

@@ -190,7 +190,7 @@ namespace SpineViewer.Spine.Implementations.Spine
         {
             vertexArray.Clear();
             states.Texture = null;
-            states.Shader = Shader.GetShader(usePremultipliedAlpha);
+            states.Shader = Shader.GetSpineShader(usePremultipliedAlpha);
 
             // 要用 DrawOrder 而不是 Slots
             foreach (var slot in skeleton.DrawOrder)

SpineViewer/Spine/Implementations/Spine/Spine38.cs

@@ -196,7 +196,7 @@ namespace SpineViewer.Spine.Implementations.Spine
         {
             vertexArray.Clear();
             states.Texture = null;
-            states.Shader = Shader.GetShader(usePremultipliedAlpha);
+            states.Shader = Shader.GetSpineShader(usePremultipliedAlpha);
 
             // 要用 DrawOrder 而不是 Slots
             foreach (var slot in skeleton.DrawOrder)

SpineViewer/Spine/Implementations/Spine/Spine40.cs

@@ -192,7 +192,7 @@ namespace SpineViewer.Spine.Implementations.Spine
         {
             vertexArray.Clear();
             states.Texture = null;
-            states.Shader = Shader.GetShader(usePremultipliedAlpha);
+            states.Shader = Shader.GetSpineShader(usePremultipliedAlpha);
 
             // 要用 DrawOrder 而不是 Slots
             foreach (var slot in skeleton.DrawOrder)

SpineViewer/Spine/Implementations/Spine/Spine41.cs

@@ -192,7 +192,7 @@ namespace SpineViewer.Spine.Implementations.Spine
         {
             vertexArray.Clear();
             states.Texture = null;
-            states.Shader = Shader.GetShader(usePremultipliedAlpha);
+            states.Shader = Shader.GetSpineShader(usePremultipliedAlpha);
 
             // 要用 DrawOrder 而不是 Slots
             foreach (var slot in skeleton.DrawOrder)

SpineViewer/Spine/Implementations/Spine/Spine42.cs

@@ -192,7 +192,7 @@ namespace SpineViewer.Spine.Implementations.Spine
         {
             vertexArray.Clear();
             states.Texture = null;
-            states.Shader = Shader.GetShader(usePremultipliedAlpha);
+            states.Shader = Shader.GetSpineShader(usePremultipliedAlpha);
 
             // 要用 DrawOrder 而不是 Slots
             foreach (var slot in skeleton.DrawOrder)

SpineViewer/Spine/Spine.cs

@@ -370,7 +370,7 @@ namespace SpineViewer.Spine
         protected abstract RectangleF bounds { get; }
 
         /// <summary>
-        /// 骨骼预览图
+        /// 骨骼预览图, 并没有去除预乘, 画面可能偏暗
         /// </summary>
         [Browsable(false)]
         public Image Preview { get; private set; }
@@ -405,8 +405,15 @@ namespace SpineViewer.Spine
 
         /// <summary>
         /// SFML.Graphics.Drawable 接口实现
+        /// <para>这个渲染实现绘制出来的像素将是预乘的, 当渲染的背景透明度是 1 时, 则等价于非预乘的结果, 即正常画面, 否则画面偏暗</para>
+        /// <para>可以用于 <see cref="SFML.Graphics.RenderWindow"/> 的渲染, 因为直接在窗口上绘制时窗口始终是不透明的</para>
         /// </summary>
         public void Draw(SFML.Graphics.RenderTarget target, SFML.Graphics.RenderStates states) { lock (_lock) draw(target, states); }
+
+        /// <summary>
+        /// 这个渲染实现绘制出来的像素将是预乘的, 当渲染的背景透明度是 1 时, 则等价于非预乘的结果, 即正常画面, 否则画面偏暗
+        /// <para>可以用于 <see cref="SFML.Graphics.RenderWindow"/> 的渲染, 因为直接在窗口上绘制时窗口始终是不透明的</para>
+        /// </summary>
         protected abstract void draw(SFML.Graphics.RenderTarget target, SFML.Graphics.RenderStates states);
 
         #endregion