From 9290acd379db6168df2c8020045171acc4a50ad2 Mon Sep 17 00:00:00 2001
From: fgenesis <false.genesis@googlemail.com>
Date: Fri, 29 Apr 2022 10:26:25 +0200
Subject: [PATCH] fix taking screenshots

---
 BBGE/Core.cpp             | 29 +++++++++++++++++++----------
 BBGE/Core.h               |  4 ++--
 ExternalLibs/tinylibs.cpp |  1 +
 3 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/BBGE/Core.cpp b/BBGE/Core.cpp
index c8fef20..225a5c1 100644
--- a/BBGE/Core.cpp
+++ b/BBGE/Core.cpp
@@ -2210,10 +2210,11 @@ bool Core::canChangeState()
 // Take a screenshot of the specified region of the screen and store it
 // in a 32bpp pixel buffer.  delete[] the returned buffer when it's no
 // longer needed.
-unsigned char *Core::grabScreenshot(int x, int y, int w, int h)
+unsigned char *Core::grabScreenshot(size_t x, size_t y, size_t w, size_t h)
 {
-	unsigned int size = sizeof(unsigned char) * w * h * 4;
-	unsigned char *imageData = new unsigned char[size];
+	const size_t N = w * h;
+	const size_t size = sizeof(unsigned char) * N * 4;
+	unsigned char * const imageData = new unsigned char[size];
 
 	glPushAttrib(GL_ALL_ATTRIB_BITS);
 	glDisable(GL_BLEND);
@@ -2232,12 +2233,20 @@ unsigned char *Core::grabScreenshot(int x, int y, int w, int h)
 
 	// Force all alpha values to 255.
 	unsigned char *c = imageData;
-	for (int x = 0; x < w; x++)
+	for (size_t i = 0; i < N; ++i, c += 4)
 	{
-		for (int y = 0; y < h; y++, c += 4)
-		{
-			c[3] = 255;
-		}
+		c[3] = 255;
+	}
+
+	// OpenGL outputs the image upside down -> flip pixel rows
+	const ptrdiff_t rowOffs = 4 * w;
+	unsigned char * row0 = imageData;
+	unsigned char * row1 = imageData + size - rowOffs;
+	while(row0 < row1)
+	{
+		std::swap_ranges(row0, row0 + rowOffs, row1);
+		row0 += rowOffs;
+		row1 -= rowOffs;
 	}
 
 	return imageData;
@@ -2245,7 +2254,7 @@ unsigned char *Core::grabScreenshot(int x, int y, int w, int h)
 }
 
 // Like grabScreenshot(), but grab from the center of the screen.
-unsigned char *Core::grabCenteredScreenshot(int w, int h)
+unsigned char *Core::grabCenteredScreenshot(size_t w, size_t h)
 {
 	return grabScreenshot(core->width/2 - w/2, core->height/2 - h/2, w, h);
 }
@@ -2253,7 +2262,7 @@ unsigned char *Core::grabCenteredScreenshot(int w, int h)
 // takes a screen shot and saves it to a TGA or PNG image
 bool Core::saveScreenshot(const std::string &filename, bool png)
 {
-	int w = getWindowWidth(), h = getWindowHeight();
+	size_t w = getWindowWidth(), h = getWindowHeight();
 	unsigned char *imageData = grabCenteredScreenshot(w, h);
 	bool ok = png
 		? pngSaveRGBA(filename.c_str(), w, h, imageData)
diff --git a/BBGE/Core.h b/BBGE/Core.h
index ee567f7..68add58 100644
--- a/BBGE/Core.h
+++ b/BBGE/Core.h
@@ -354,8 +354,8 @@ public:
 		return virtualHeight;
 	}
 
-	unsigned char *grabScreenshot(int x, int y, int w, int h);
-	unsigned char *grabCenteredScreenshot(int w, int h);
+	unsigned char *grabScreenshot(size_t x, size_t y, size_t w, size_t h);
+	unsigned char *grabCenteredScreenshot(size_t w, size_t h);
 	bool saveScreenshot(const std::string &filename, bool png);
 
 	bool minimized;
diff --git a/ExternalLibs/tinylibs.cpp b/ExternalLibs/tinylibs.cpp
index 50eb40c..6eebcb7 100644
--- a/ExternalLibs/tinylibs.cpp
+++ b/ExternalLibs/tinylibs.cpp
@@ -19,6 +19,7 @@ static unsigned char * miniz_stbi_compress(unsigned char *data, int data_len, in
 			return NULL;
 		}
 	}
+	*out_len = (int)maxsz;
 	return packed;
 }