Merge pull request #59 from nut-tree/feature/183/windows_high_dpi

(nut-tree/nut.js/183) Determine scale factor ifor high DPI displays i…

Author: s1hofmann

src/win32/screengrab.c

@@ -2,6 +2,22 @@
 #include "../endian.h"
 #include <stdlib.h> /* malloc() */
 
+MMRect getScaledRect(MMRect input, HDC imageSource) {
+	BITMAP structBitmapHeader;
+	memset( &structBitmapHeader, 0, sizeof(BITMAP) );
+
+	HGDIOBJ hBitmap = GetCurrentObject(imageSource, OBJ_BITMAP);
+	GetObject(hBitmap, sizeof(BITMAP), &structBitmapHeader);
+
+	size_t desktopWidth = (size_t)GetSystemMetrics(SM_CXSCREEN);
+	size_t desktopHeight = (size_t)GetSystemMetrics(SM_CYSCREEN);
+
+	double scaleX = (double)(structBitmapHeader.bmWidth / desktopWidth);
+	double scaleY = (double)(structBitmapHeader.bmHeight / desktopHeight);
+
+	return MMRectMake(input.origin.x, input.origin.y, input.size.width * scaleX, input.size.height * scaleY);
+}
+
 MMBitmapRef copyMMBitmapFromDisplayInRect(MMRect rect)
 {
 	MMBitmapRef bitmap;
@@ -10,22 +26,24 @@ MMBitmapRef copyMMBitmapFromDisplayInRect(MMRect rect)
 	HBITMAP dib;
 	BITMAPINFO bi;
 
+	screen = GetWindowDC(NULL); /* Get entire screen */
+	MMRect scaledRect = getScaledRect(rect, screen);
+
+	if (screen == NULL) return NULL;
+
 	/* Initialize bitmap info. */
 	bi.bmiHeader.biSize = sizeof(bi.bmiHeader);
-   	bi.bmiHeader.biWidth = (long)rect.size.width;
-   	bi.bmiHeader.biHeight = -(long)rect.size.height; /* Non-cartesian, please */
+   	bi.bmiHeader.biWidth = (long)scaledRect.size.width;
+   	bi.bmiHeader.biHeight = -(long)scaledRect.size.height; /* Non-cartesian, please */
    	bi.bmiHeader.biPlanes = 1;
    	bi.bmiHeader.biBitCount = 32;
    	bi.bmiHeader.biCompression = BI_RGB;
-   	bi.bmiHeader.biSizeImage = (DWORD)(4 * rect.size.width * rect.size.height);
+   	bi.bmiHeader.biSizeImage = (DWORD)(4 * scaledRect.size.width * scaledRect.size.height);
 	bi.bmiHeader.biXPelsPerMeter = 0;
 	bi.bmiHeader.biYPelsPerMeter = 0;
 	bi.bmiHeader.biClrUsed = 0;
 	bi.bmiHeader.biClrImportant = 0;
 
-	screen = GetDC(NULL); /* Get entire screen */
-	if (screen == NULL) return NULL;
-
 	/* Get screen data in display device context. */
    	dib = CreateDIBSection(screen, &bi, DIB_RGB_COLORS, &data, NULL, 0);
 
@@ -35,11 +53,11 @@ MMBitmapRef copyMMBitmapFromDisplayInRect(MMRect rect)
 	    !BitBlt(screenMem,
 	            (int)0,
 	            (int)0,
-	            (int)rect.size.width,
-	            (int)rect.size.height,
+	            (int)scaledRect.size.width,
+	            (int)scaledRect.size.height,
 				screen,
-				(int)rect.origin.x,
-				(int)rect.origin.y,
+				(int)scaledRect.origin.x,
+				(int)scaledRect.origin.y,
 				SRCCOPY)) {
 
 		/* Error copying data. */
@@ -51,9 +69,9 @@ MMBitmapRef copyMMBitmapFromDisplayInRect(MMRect rect)
 	}
 
 	bitmap = createMMBitmap(NULL,
-	                        rect.size.width,
-	                        rect.size.height,
-	                        4 * rect.size.width,
+	                        scaledRect.size.width,
+	                        scaledRect.size.height,
+	                        4 * scaledRect.size.width,
 	                        (uint8_t)bi.bmiHeader.biBitCount,
 	                        4);