Comparer: alpha-blended overlay, larger cells, 'D' toggle

- Grid cells widened from 24px to 48px on screen so dots are less dense.
- Each differing cell now shows both a translucent rectangle outline and
  a center dot, drawn with GDI+ alpha blending over the source image.
- 'D' key toggles the overlay on and off; default is on.

Author: chammoru

Comparer/Comparer.cpp

@@ -9,6 +9,9 @@
 
 #include "ComparerDoc.h"
 
+#include <gdiplus.h>
+#pragma comment(lib, "gdiplus.lib")
+
 #ifdef _DEBUG
 #define new DEBUG_NEW
 #endif
@@ -62,6 +65,9 @@ BOOL CComparerApp::InitInstance()
 {
 	CWinApp::InitInstance();
 
+	Gdiplus::GdiplusStartupInput gdiplusStartupInput;
+	Gdiplus::GdiplusStartup(&mGdiplusToken, &gdiplusStartupInput, NULL);
+
 	SetRegistryKey(_T("Chammoru"));
 	LoadStdProfileSettings(4);  // Load standard INI file options (including MRU)
 
@@ -108,6 +114,12 @@ BOOL CComparerApp::InitInstance()
 	return TRUE;
 }
 
+int CComparerApp::ExitInstance()
+{
+	Gdiplus::GdiplusShutdown(mGdiplusToken);
+	return CWinApp::ExitInstance();
+}
+
 
 
 // CAboutDlg dialog used for App About

Comparer/Comparer.h

@@ -24,11 +24,15 @@ class CComparerApp : public CWinApp
 // Overrides
 public:
 	virtual BOOL InitInstance();
+	virtual int ExitInstance();
 
 // Implementation
 	afx_msg void OnAppAbout();
 	DECLARE_MESSAGE_MAP()
 	afx_msg void OnFileOpen();
+
+private:
+	ULONG_PTR mGdiplusToken;
 };
 
 extern CComparerApp theApp;

Comparer/ComparerDoc.cpp

@@ -64,6 +64,7 @@ CComparerDoc::CComparerDoc()
 , mFps(COMPARER_DEF_FPS)
 , mInterpol(false)
 , mDiffRes(false)
+, mDiffOverlay(true)
 {
 	BITMAPINFOHEADER &bmiHeader = mBmi.bmiHeader;
 	bmiHeader.biSize = (DWORD)sizeof(BITMAPINFOHEADER);

Comparer/ComparerDoc.h

@@ -79,6 +79,7 @@ class CComparerDoc : public CDocument
 	double mFps;
 	bool mInterpol;
 	bool mDiffRes;
+	bool mDiffOverlay;
 
 // Operations
 public:

Comparer/ComparerView.cpp

@@ -16,6 +16,8 @@
 #include <QViewerCmn.h>
 #include <QImageStr.h>
 
+#include <gdiplus.h>
+
 // CComparerView
 
 CComparerView::CComparerView()
@@ -249,12 +251,15 @@ void CComparerView::OnDraw(CDC *pDC)
 	mProcessing = false;
 }
 
-// Pilot: draw a pink dot in every grid cell that contains at least one pixel
-// that differs from the reference pane. Cell size is fixed in display pixels,
-// so zooming in implicitly subdivides the source region each cell covers —
-// at maximum zoom the dot resolves to an individual differing pixel.
+// Pilot: draw a semi-transparent pink cell outline + center dot in every
+// grid cell that contains at least one pixel that differs from the reference
+// pane. Cell size is fixed in display pixels, so zooming in implicitly
+// subdivides the source region each cell covers — at maximum zoom each dot
+// resolves to a single differing source pixel.
 void CComparerView::DrawDiffOverlay(CDC *pDC, CComparerDoc *pDoc, ComparerPane *pane)
 {
+	if (!pDoc->mDiffOverlay)
+		return;
 	if (!pane || !pane->isAvail() || !pane->rgbBuf)
 		return;
 
@@ -276,21 +281,24 @@ void CComparerView::DrawDiffOverlay(CDC *pDC, CComparerDoc *pDoc, ComparerPane *
 	const BYTE *bufA = pane->rgbBuf;
 	const BYTE *bufB = other->rgbBuf;
 
-	const int cellPx  = 24;          // grid cell size in display pixels
-	const int dotR    = 3;           // dot radius
-	const COLORREF kPink = RGB(0xff, 0x3d, 0x8a);
+	const int cellPx = 48;   // grid cell size in display pixels
+	const int dotR   = 3;    // center dot radius
+
+	Gdiplus::Graphics g(pDC->m_hDC);
+	g.SetSmoothingMode(Gdiplus::SmoothingModeAntiAlias);
+	g.SetCompositingMode(Gdiplus::CompositingModeSourceOver);
 
-	CBrush dotBrush(kPink);
-	CBrush *prevBrush = pDC->SelectObject(&dotBrush);
-	HGDIOBJ prevPen   = pDC->SelectObject(::GetStockObject(NULL_PEN));
+	const Gdiplus::Color cellColor(110, 0xff, 0x3d, 0x8a);   // ~43% alpha pink
+	const Gdiplus::Color dotColor (220, 0xff, 0x3d, 0x8a);   // ~86% alpha pink
+	Gdiplus::Pen        cellPen(cellColor, 1.5f);
+	Gdiplus::SolidBrush dotBrush(dotColor);
 
 	const float invN = (pDoc->mN > 0.0f) ? (1.0f / pDoc->mN) : 1.0f;
 
 	for (int cy = 0; cy < mHCanvas; cy += cellPx) {
 		int cellBot = cy + cellPx;
 		if (cellBot > mHCanvas) cellBot = mHCanvas;
 
-		// Map canvas y range -> source y range.
 		int sy0 = (int)floorf((cy      - mYDst) * invN);
 		int sy1 = (int)ceilf ((cellBot - mYDst) * invN);
 		if (sy0 < 0)         sy0 = 0;
@@ -307,7 +315,6 @@ void CComparerView::DrawDiffOverlay(CDC *pDC, CComparerDoc *pDoc, ComparerPane *
 			if (sx1 > pDoc->mW) sx1 = pDoc->mW;
 			if (sx0 >= sx1)     continue;
 
-			// Scan the source rectangle for any differing byte; early exit.
 			bool hasDiff = false;
 			const int byteStart = sx0 * QIMG_DST_RGB_BYTES;
 			const int byteLen   = (sx1 - sx0) * QIMG_DST_RGB_BYTES;
@@ -321,16 +328,17 @@ void CComparerView::DrawDiffOverlay(CDC *pDC, CComparerDoc *pDoc, ComparerPane *
 			}
 
 			if (hasDiff) {
-				int dotX = (cx + cellRight) / 2;
-				int dotY = (cy + cellBot)   / 2;
-				pDC->Ellipse(dotX - dotR, dotY - dotR,
-				             dotX + dotR + 1, dotY + dotR + 1);
+				g.DrawRectangle(&cellPen,
+					cx + 0.5f, cy + 0.5f,
+					(float)(cellRight - cx - 1), (float)(cellBot - cy - 1));
+
+				float dotX = (cx + cellRight) * 0.5f;
+				float dotY = (cy + cellBot)   * 0.5f;
+				g.FillEllipse(&dotBrush,
+					dotX - dotR, dotY - dotR, 2.0f * dotR, 2.0f * dotR);
 			}
 		}
 	}
-
-	pDC->SelectObject(prevBrush);
-	pDC->SelectObject(prevPen);
 }
 
 void CComparerView::DrawEmptyPane(CDC *pDC, CComparerDoc *pDoc)
@@ -764,6 +772,9 @@ void CComparerView::OnKeyDown(UINT nChar, UINT nRepCnt, UINT nFlags)
 		pDoc->mInterpol = !pDoc->mInterpol;
 		Invalidate(FALSE);
 		break;
+	case 'D':
+		pDoc->mDiffOverlay = !pDoc->mDiffOverlay;
+		break;
 	}
 
 	// Most shortcuts affect shared document/view state, so refresh once at the end.