Lost transparency in SDL surfaces drawn manually

Posted by Christian Ivicevic on Game Development See other posts from Game Development or by Christian Ivicevic
Published on 2012-09-10T18:06:07Z Indexed on 2012/09/10 21:50 UTC
Read the original article Hit count: 466

Filed under:

rendering

|

sdl

|

image

|

transparency

I want to create SDL_Surface objects for each layer of my 2d tile-based map so that I have to render only one surface per layer rather than too many tiles. With normal tiles which do not have transparent areas this works well, however I am not able to create a SDL_Surface with transparent pixels everywhere to be able to draw some tiles on specific parts which should be visible (I do NOT want the whole surface to appear with a specific opacity - I want to create overlaying tiles where one can look through).

Currently I am creating my layers like this to draw with SDL_BlitSurface on them:

SDL_Surface* layer =
    SDL_CreateRGBSurface(
        SDL_HWSURFACE | SDL_SRCALPHA,
        layerWidth, layerHeight, 32, 0, 0, 0, 0);

If you have a look at this screenshot I have provided here

Transparency Fail

you can see that the bottom layer with no transparent parts gets rendered correctly. However the overlay with the tree tile (which is transparent in the top left corner) is drawn own its own surface which is black and not transparent as expected. The expected result (concerning the transparency) can be seen here

Expected transparency

Can anyone explain me how to handle surfaces which are actually transparent rather than drawing all my overlay tiles separately?

© Game Development or respective owner

Related posts about rendering

Optimizing transition/movement smoothness for a 2D flash game.

as seen on Stack Overflow - Search for 'Stack Overflow'
Update 6: Fenomenas suggested me to re-create everything as simple as possible. I had my doubts that this would make any difference as the algorithm remains the same, and performance did not seem to be the issue. Anyway, it was the only suggestion I got so here it is: 30 FPS: http://www.feedpostal… >>> More
iphone Rendering 3-D Object rendering

as seen on Stack Overflow - Search for 'Stack Overflow'
Hello, I'm a beginner 3-D Quartz thing but knows how to create application. I was looking over sample of GLGravity Source code given by apple today, I was wondering teapot.h file contains all contents of array file such as indices, vertices. Do you guys think this code has been provided by human or… >>> More
Delay rendering or force re-rendering in Flex

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi there, In my Flex application, using a custom control, I am making a JSON request to grab some data from the server. My rendering depends on this data such as knowing how many boxes to draw. How can I either force the rendering to wait until I've got the data before drawing to screen or have the… >>> More
Rendering ASP.NET Script References into the Html Header

as seen on West-Wind - Search for 'West-Wind'
One thing that I’ve come to appreciate in control development in ASP.NET that use JavaScript is the ability to have more control over script and script include placement than ASP.NET provides natively. Specifically in ASP.NET you can use either the ClientScriptManager or ScriptManager to embed scripts… >>> More
Rendering in WebKit

as seen on Google Code - Search for 'Google Code'
Rendering in WebKit A deep dive into the guts of webkit. Eric Seidel explains the process from loading the resources, building the DOM tree, and the various trees involved in rendering. From: GoogleDevelopers Views: 4525 26 ratings Time: 34:45 More in Science & Technology >>> More

Related posts about sdl

Compiling SDL under Windows with sdl-config

as seen on Game Development - Search for 'Game Development'
I have downloaded NXEngine (The Open Source version of Cave Story). I have a make file in the directory, which I execute using msys. However, the make file uses sdl-config: g++ -g -O2 -c main.cpp -D DEBUG `sdl-config --cflags` -Wreturn-type -Wformat -Wno-multichar -o main.o /bin/sh: sdl-config: command… >>> More
How can I get the palette of an 8-bit surface in SDL.NET/Tao.SDL?

as seen on Game Development - Search for 'Game Development'
I'm looking to get the palette of an 8-bit surface in SDL.NET if possible, or (more than likely) using Tao.SDL. This is because I want to do palette swapping with the palette directly, instead of blitting surfaces together to replace colours like how you would do it with a 32-bit surface. I've gotten… >>> More
Using SDL to replace colors using SDL Color Keys

as seen on Stack Overflow - Search for 'Stack Overflow'
Hey, I am working an a simple Roguelike game, and using SDL as the display. The Graphics for the game is an image of Codepage 437, with the background being black, and the font white. Instead of using many seperate image files that are already colored, I want to use one image file, and replace… >>> More
Where is sdl-config installed on MacOS 10.6 (Snow Leopard)

as seen on Stack Overflow - Search for 'Stack Overflow'
After installing SDL and SDL-devel in MacOS X 10.6 (Snow Leopard), trying to configure some source code that requires SDL yields: checking for sdl-config... no checking for SDL - version >= 1.2.0... no *** The sdl-config script installed by SDL could not be found *** If SDL was installed in PREFIX… >>> More
Implementing the Security Development Lifecycle (SDL) at a Large Insurance Company

as seen on Dot net Slackers - Search for 'Dot net Slackers'
Find out how Cigital, an SDL Pro Network member, assisted a large insurance company adopt the Microsoft SDL. The case study describes both the business drivers leading up to the company's recognizing the need for incorporating the SDL within their development process as well as the initial roll out… >>> More