BGE: alpha on frame buffer and precedence of MSAA over swap.

A new option '-a' can be passed to the blenderplayer. It forces the
framebuffer to have an alpha channel.
This can be used in VideoTexture to return a image with alpha channel
with ImageViewport (provided alpha is set to True on the ImageViewport
object and that the background color alpha channel is 0, which is the
default).
Without the -a option, the frame buffer has no alpha channel and
ImageViewport always returns an opaque image, no matter what.
In Linux, the player window will be rendered transparently over
the desktop.
In Windows, the player window is still rendered opaque because
transparency of the window is only possible using the 'compositing'
functions of Windows. The code is there but not enabled  (look for
WIN32_COMPOSITING) because 1) it doesn't work so well 2) it requires
a DLL that is only available on Vista and up.

give precedence to AA over Swap copy:

Certain GPU (intel) will not allow MSAA together with swap copy.
Previously, swap copy had priority over MSAA: fewer AA samples would be
chosen if it was the condition to get swap copy. This patch reverse the
logic: swap copy will be abandonned if another swap method (undefined or
exchange) will provide the number of AA samples requested. If no AA
samples is requested, swap copy still has the priority of course.

1 files changed, 13 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b558fe14820..15ee8349f39 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -273,6 +273,7 @@ endif()
 if(WITH_X11)
 	option(WITH_X11_XINPUT    "Enable X11 Xinput (tablet support and unicode input)"  ON)
 	option(WITH_X11_XF86VMODE "Enable X11 video mode switching"                       ON)
+	option(WITH_X11_ALPHA     "Enable X11 transparent background"                     ON)
 endif()
 
 if(UNIX AND NOT APPLE)
@@ -723,6 +724,7 @@ if(WITH_GHOST_SDL OR WITH_HEADLESS)
 	set(WITH_X11           OFF)
 	set(WITH_X11_XINPUT    OFF)
 	set(WITH_X11_XF86VMODE OFF)
+	set(WITH_X11_ALPHA     OFF)
 	set(WITH_GHOST_XDND    OFF)
 	set(WITH_INPUT_IME     OFF)
 endif()
@@ -862,6 +864,16 @@ if(WITH_X11)
 		endif()
 	endif()
 
+	if(WITH_X11_ALPHA)
+		find_library(X11_Xrender_LIB Xrender  ${X11_LIB_SEARCH_PATH})
+		mark_as_advanced(X11_Xrender_LIB)
+		if (X11_Xrender_LIB)
+			list(APPEND PLATFORM_LINKLIBS ${X11_Xrender_LIB})
+		else()
+			set(WITH_X11_ALPHA OFF)
+		endif()
+	endif()
+
 endif()
 
 
@@ -3199,6 +3211,7 @@ if(FIRST_RUN)
 
 	info_cfg_text("System Options:")
 	info_cfg_option(WITH_INSTALL_PORTABLE)
+	info_cfg_option(WITH_X11_ALPHA)
 	info_cfg_option(WITH_X11_XF86VMODE)
 	info_cfg_option(WITH_X11_XINPUT)
 	info_cfg_option(WITH_MEM_JEMALLOC)