diff --git a/src/video/opengl.cpp b/src/video/opengl.cpp
--- a/src/video/opengl.cpp
+++ b/src/video/opengl.cpp
@@ -24,6 +24,7 @@
 
 #include "opengl.h"
 #include "../core/mem_func.hpp"
+#include "../core/geometry_func.hpp"
 #include "../gfx_func.h"
 #include "../debug.h"
 
@@ -292,8 +293,9 @@ bool OpenGLBackend::Resize(int w, int h,
 
 /**
  * Render video buffer to the screen.
+ * @param update_rect Rectangle encompassing the dirty region of the video buffer.
  */
-void OpenGLBackend::Paint()
+void OpenGLBackend::Paint(Rect update_rect)
 {
 	assert(this->vid_buffer != nullptr);
 
@@ -301,8 +303,10 @@ void OpenGLBackend::Paint()
 
 	/* Update changed rect of the video buffer texture. */
 	glBindTexture(GL_TEXTURE_2D, this->vid_texture);
-	glPixelStorei(GL_UNPACK_ROW_LENGTH, _screen.pitch);
-	glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, _screen.width, _screen.height, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV, this->vid_buffer);
+	if (!IsEmptyRect(update_rect)) {
+		glPixelStorei(GL_UNPACK_ROW_LENGTH, _screen.pitch);
+		glTexSubImage2D(GL_TEXTURE_2D, 0, update_rect.left, update_rect.top, update_rect.right - update_rect.left, update_rect.bottom - update_rect.top, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV, (uint32 *)this->vid_buffer + update_rect.top * _screen.pitch + update_rect.left);
+	}
 
 	/* Blit video buffer to screen. */
 	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
diff --git a/src/video/opengl.h b/src/video/opengl.h
--- a/src/video/opengl.h
+++ b/src/video/opengl.h
@@ -13,6 +13,7 @@
 #define VIDEO_OPENGL_H
 
 #include "../core/alloc_type.hpp"
+#include "../core/geometry_type.hpp"
 
 typedef void (*OGLProc)();
 typedef OGLProc (*GetOGLProcAddressProc)(const char *proc);
@@ -42,7 +43,7 @@ public:
 	static void Destroy();
 
 	bool Resize(int w, int h, bool force = false);
-	void Paint();
+	void Paint(Rect update_rect);
 
 	/**
 	 * Get a pointer to the memory for the video driver to draw to.
diff --git a/src/video/win32_v.cpp b/src/video/win32_v.cpp
--- a/src/video/win32_v.cpp
+++ b/src/video/win32_v.cpp
@@ -64,8 +64,6 @@ static std::condition_variable_any *_dra
 static volatile bool _draw_continue;
 /** Local copy of the palette for use in the drawing thread. */
 static Palette _local_palette;
-/** Region of the screen that needs redrawing. */
-static Rect _dirty_rect;
 
 bool VideoDriver_Win32Base::ClaimMousePointer()
 {
@@ -886,7 +884,7 @@ void VideoDriver_Win32Base::Stop()
 void VideoDriver_Win32Base::MakeDirty(int left, int top, int width, int height)
 {
 	Rect r = {left, top, left + width, top + height};
-	_dirty_rect = BoundingRect(_dirty_rect, r);
+	this->dirty_rect = BoundingRect(this->dirty_rect, r);
 }
 
 void VideoDriver_Win32Base::CheckPaletteAnim()
@@ -1243,7 +1241,7 @@ void VideoDriver_Win32GDI::Paint()
 {
 	PerformanceMeasurer framerate(PFE_VIDEO);
 
-	if (IsEmptyRect(_dirty_rect)) return;
+	if (IsEmptyRect(this->dirty_rect)) return;
 
 	HDC dc = GetDC(this->main_wnd);
 	HDC dc2 = CreateCompatibleDC(dc);
@@ -1279,7 +1277,7 @@ void VideoDriver_Win32GDI::Paint()
 
 	ReleaseDC(this->main_wnd, dc);
 
-	_dirty_rect = {};
+	this->dirty_rect = {};
 }
 
 void VideoDriver_Win32GDI::PaintThread()
@@ -1446,6 +1444,8 @@ bool VideoDriver_Win32OpenGL::AllocateBa
 
 	if (this->gl_rc == nullptr) return false;
 
+	this->dirty_rect = {};
+
 	bool res = OpenGLBackend::Get()->Resize(w, h);
 	_wnd.buffer_bits = OpenGLBackend::Get()->GetVideoBuffer();
 	return res;
@@ -1455,6 +1455,8 @@ void VideoDriver_Win32OpenGL::Paint()
 {
 	PerformanceMeasurer framerate(PFE_VIDEO);
 
+	if (IsEmptyRect(this->dirty_rect)) return;
+
 	if (_cur_palette.count_dirty != 0) {
 		Blitter *blitter = BlitterFactory::GetCurrentBlitter();
 
@@ -1473,8 +1475,10 @@ void VideoDriver_Win32OpenGL::Paint()
 		_cur_palette.count_dirty = 0;
 	}
 
-	OpenGLBackend::Get()->Paint();
+	OpenGLBackend::Get()->Paint(this->dirty_rect);
 	SwapBuffers(this->dc);
+
+	this->dirty_rect = {};
 }
 
 #endif /* WITH_OPENGL */
diff --git a/src/video/win32_v.h b/src/video/win32_v.h
--- a/src/video/win32_v.h
+++ b/src/video/win32_v.h
@@ -38,6 +38,7 @@ public:
 protected:
 	HWND    main_wnd;      ///< Handle to system window.
 	bool    fullscreen;    ///< Whether to use (true) fullscreen mode.
+	Rect    dirty_rect;    ///< Region of the screen that needs redrawing.
 
 	Dimension GetScreenSize() const override;
 	float GetDPIScale() override;