From 9af7575d2bd79593983431b493b63c08d41e7e20 Mon Sep 17 00:00:00 2001
From: Takaranoao <takaranoao@gmail.com>
Date: Thu, 3 Apr 2025 21:28:13 +0800
Subject: [PATCH] =?UTF-8?q?bitblt=20=E8=BF=98=E8=83=BD=E6=9B=B4=E5=BF=AB?=
 =?UTF-8?q?=20(#1395)?=
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* Bitblt:GDI直接返回转换后的位图，不再由CV二次转换

* update documentation for clarity

* typo
---
 Fischless.GameCapture/BitBlt/BitBltCapture.cs | 47 ++++++++++++++-----
 Fischless.GameCapture/BitBlt/BitBltSession.cs | 32 ++++++++++---
 2 files changed, 60 insertions(+), 19 deletions(-)

diff --git a/Fischless.GameCapture/BitBlt/BitBltCapture.cs b/Fischless.GameCapture/BitBlt/BitBltCapture.cs
index bf8eff15..85992d13 100644
--- a/Fischless.GameCapture/BitBlt/BitBltCapture.cs
+++ b/Fischless.GameCapture/BitBlt/BitBltCapture.cs
@@ -92,7 +92,7 @@ public class BitBltCapture : IGameCapture
         }
         catch (Exception e)
         {
-            Error.WriteLine("Failed to create bitblt session:{0}", e);
+            Error.WriteLine("[BitBlt]Failed to create session:{0}", e);
             return false;
         }
         finally
@@ -123,27 +123,48 @@ public class BitBltCapture : IGameCapture
             }
         }
 
+        Mat? mat = null;
         try
         {
             _lockSlim.EnterReadLock();
-            using var mat = _session?.BitBlt();
-            if (mat is null || mat.Empty())
+            if (_session is null)
             {
-                if (_session is not null && !_session.IsInvalid())
-                {
-                    // 有时候会出现截图失败的情况，这时候重置会话
-                    _needResetSession = true;
-                }
-
+                // 没有成功创建会话，直接返回空
                 return null;
             }
+            mat = _session.GetMat();
+            
+            if (mat is not null) // 成功执行
+            {
+                if (!mat.Empty()) // 并且获取到了图
+                {
+                    _needResetSession = false;
+                    return mat;
+                }
+                else // 成功执行但是没有图，可能是截图过快导致的
+                {
+                    mat.Dispose();
+                    mat = null; // 防止二次释放
+                }
+            }
 
-            var bgrMat = new Mat();
-            Cv2.CvtColor(mat, bgrMat, ColorConversionCodes.BGRA2BGR);
-            return bgrMat;
+            // 无论没有图还是执行失败都会到这里
+            if (_session is not null && !_session.IsInvalid())
+            {
+                // _session正确但是截图失败，如果持续出现这个问题需要重置会话
+                _needResetSession = true;
+            }
+
+            return null;
         }
-        catch (Exception)
+        catch (Exception e)
         {
+            // 理论这里不应出现异常，除非窗口不存在了或者有什么bug
+            // 出现异常的时候释放内存
+            mat?.Dispose();
+            // 如果持续出现异常则重置会话
+            _needResetSession = true;
+            Error.WriteLine("[BitBlt]Failed to capture image {0}", e);
             return null;
         }
         finally
diff --git a/Fischless.GameCapture/BitBlt/BitBltSession.cs b/Fischless.GameCapture/BitBlt/BitBltSession.cs
index 6d102f71..ff3efee7 100644
--- a/Fischless.GameCapture/BitBlt/BitBltSession.cs
+++ b/Fischless.GameCapture/BitBlt/BitBltSession.cs
@@ -25,8 +25,18 @@ public class BitBltSession : IDisposable
     // 旧位图，析构时一起释放掉
     private HGDIOBJ _oldBitmap;
     public int Width { get; }
+
     public int Height { get; }
 
+    // 用于过滤alpha通道
+    private static readonly Gdi32.BLENDFUNCTION BlendFunction = new()
+    {
+        BlendOp = 0, //Gdi32.BlendOperation.AC_SRC_OVER,
+        BlendFlags = 0,
+        SourceConstantAlpha = 255,
+        AlphaFormat = 0,
+    };
+
     private readonly object _lockObject = new object();
 
 
@@ -71,9 +81,9 @@ public class BitBltSession : IDisposable
                         biWidth = Width,
                         biHeight = -Height, // Top-down image
                         biPlanes = 1,
-                        biBitCount = 32,
+                        biBitCount = 24,
                         biCompression = 0, // BI_RGB
-                        biSizeImage = 0
+                        biSizeImage = 0,
                     }
                 };
                 _hBitmap = Gdi32.CreateDIBSection(_hdcDest, bmi, Gdi32.DIBColorMode.DIB_RGB_COLORS, out var bits,
@@ -105,17 +115,27 @@ public class BitBltSession : IDisposable
     }
 
     /// <summary>
-    /// 调用bitblt复制并返回新的mat
+    /// 调用GDI复制到缓冲区并返回新的mat
     /// </summary>
-    /// <returns></returns>
-    public Mat? BitBlt()
+    /// <returns>MatType.CV_8UC3</returns>
+    public Mat? GetMat()
     {
         lock (_lockObject)
         {
-            return Gdi32.BitBlt(_hdcDest, 0, 0, Width, Height, _hdcSrc, 0, 0, Gdi32.RasterOperationMode.SRCCOPY) ? Mat.FromPixelData(Height, Width, MatType.CV_8UC4, _bitsPtr) : null;
+            // 直接返回转换后的位图
+            return Gdi32.AlphaBlend(_hdcDest, 0, 0, Width, Height, _hdcSrc, 0, 0, Width, Height, BlendFunction)
+                ? Mat.FromPixelData(Height, Width, MatType.CV_8UC3, _bitsPtr, (Width * 3 + 3) & ~3)
+                : null;
+
+            // 原始宏 ((((biWidth * biBitCount) + 31) & ~31) >> 3) => (biWidth * biBitCount + 3) & ~3) (在总位数是8的倍数时，两者等价)
+            // 对齐 https://learn.microsoft.com/zh-cn/windows/win32/api/wingdi/ns-wingdi-bitmapinfoheader
+
+            //  适用于32位(RGBA)
+            //  return Gdi32.BitBlt(_hdcDest, 0, 0, Width, Height, _hdcSrc, 0, 0, Gdi32.RasterOperationMode.SRCCOPY ) ? Mat.FromPixelData(Height, Width, MatType.CV_8UC3, _bitsPtr) : null;
         }
     }
 
+
     /// <summary>
     /// 不是所有的失效情况都能被检测到
     ///