9. July 2017

SDL2_image for Android with PNG image format

In the previous article, we were discussing how to add support for XPM image format to SDL2 application for Android. Let’s add other more common format. What about Portable Network Graphic (a.k.a. PNG)?

The first step is to enable PNG in SDL2_image. Just add a proper define to SDL2_image/build.gradle.

ndk {

Unfortunately, it’s not that simple. PNG support has a dependency on PNG library with a patch and PNG library has a dependency on ZIP library. In order to get PNG working you need to add these two C libraries into the project. The approach is the same like when adding SDL2_image. Each library is stored as a separate module in the directory with the same name like module name.

Register modules in settings.gradle:

include ':SDL2_image'
include ':png'
include ':zip'

Each module has it’s own build.gradle: png/build.gradle, zip/build.gradle.

You can verify compilation of the whole suite by following commands:

gradle :zip:distributeLib
gradle :png:distributeLib
gradle :SDL2_image:distributeLib

Libraries are ready. Now it’s necessary to add PNG file to the project. The location for graphic assets is app/src/main/assets.

Here is a sample code for loading and displaying PNG image:

SDL_Surface *loadedSurface = IMG_Load("smiley.png");
SDL_Texture *smileyTexture = SDL_CreateTextureFromSurface(renderer, loadedSurface);
SDL_RenderCopy(renderer, smileyTexture, NULL, NULL);

Result looks like this:

As you can see the PNG version of smiley has support for background transparency.

You can find whole source code at https://github.com/georgik/sdl2-android-example.

We will discuss how to use further SDL2 libraries in next articles. You can find more under topic SDL2.

8. July 2017

SDL2_image for Android with XPM image format

In the previous article, we were discussing how to start building SDL2 application for Android. Let’s add some images.

SDL2 library does not contain support for any image formats, you have to add further library SDL2_image which has support for several formats.

In order to add SDL2_image into Android project it is necessary to add a new module to settings.gradle:

include ':SDL2_image'

The module itself will be stored in SDL2_image directory with build.gradle which contains reference to main SDL2 library:

model {
    repositories {
        libs(PrebuiltLibraries) {
            SDL2 {
                headers.srcDir "../SDL2/include"
                binaries.withType(SharedLibraryBinary) {
                    sharedLibraryFile = file("${lib_distribution_root}/SDL2/lib/${targetPlatform.getName()}/libSDL2.so")

SDL2_image has support for several formats. You need to turn them on based on your requirements. It’s easy, just add proper define to compiler. Let’s start with simplest format XPM:

ndk { 

X PixMap (or XPM) is very simple image format which could be embedded directly into the source code.

static char * icon_xpm[] = {
        "32 23 3 1",
        "     c #FFFFFF",
        ".    c #000000",
        "+    c #FFFF00",
        "                                ",
        "            ........            ",
        "          ..++++++++..          ",
        "         .++++++++++++.         ",
        "        .++++++++++++++.        ",
        "       .++++++++++++++++.       ",
        "      .++++++++++++++++++.      ",
        "      .+++....++++....+++.      ",
        "     .++++.. .++++.. .++++.     ",
        "     .++++....++++....++++.     ",
        "     .++++++++++++++++++++.     ",
        "     .++++++++++++++++++++.     ",
        "     .+++++++++..+++++++++.     ",
        "     .+++++++++..+++++++++.     ",
        "     .++++++++++++++++++++.     ",
        "      .++++++++++++++++++.      ",
        "      .++...++++++++...++.      ",
        "       .++............++.       ",
        "        .++..........++.        ",
        "         .+++......+++.         ",
        "          ..++++++++..          ",
        "            ........            ",
        "                                "}

The next step is to transform XPM from the source code into memory structure which could be rendered on the screen.

SDL_Surface *surface;
surface = IMG_ReadXPMFromArray(icon_xpm);
texture = SDL_CreateTextureFromSurface(renderer, surface);

The last part is to call render function. You can find whole source code at https://github.com/georgik/sdl2-android-example.

We will discuss how to use further SDL2 libraries in next articles. You can find more under topic SDL2.

5. July 2017

SDL2 application for Android built by Gradle 4

SDL2 is a well known library for making games or interactive application for Linux, Windows or macOS. The library has also support for mobile devices. Building application for Android requires a little bit more effort than build for desktops.

Let’s go step-by-step.

First of all download Gradle 4 and add bin directory with gradle to your PATH environment variable.

Download and install Android Studio.

Clone sdl2-android-example project from GitHub.

Open the repo in Android Studio and open SDK Manager. Go to Tools, select menu Android, and select item SDK Manager.

In the lower right corner check option Show Package Details. Install Android SDK Build Tool e.g. version 25.0.3 and NDK.

When you open the sdl2-android-example you will see following structure. There are two gradle files in the top level directory. The first is build.gradle. The file contains a dependency on gradle-experimental plugin which is recommended for NDK builds for Android.

buildscript {
    repositories {
    dependencies {
        // Android native build plugin compatible with Gradle 4
        classpath 'com.android.tools.build:gradle-experimental:0.11.0-alpha-preview-02'

allprojects {
    repositories {

The second Gradle file is settings.gradle. The file contains a list of modules which are in the project. One module is SDL2 library. Then there are two further modules app and main. The app module is the bridge between Java and SDL2. The main module contains C code for the application.

gradle.ext.sdkVersion = 21

include ':app'
include ':SDL2'
include ':main'

These two files provide a skeleton for the build of the application. Each module SDL2, app and main are stored in the directory that matches the name a of module. Each module contains its own build.gradle which describes how to build the module.

The module file SDL2/build.gradle is interesting because it contains many excludes. It does not make sense to build all C files from SDL2 for Android.

The module file main/build.gradle contains information for linking the C application with SDL2 library.

The module file app/build.gradle contains information how to wrap all the C source code into final application.

First of all, it is necessary to build the library:

gradle SDL2:distributeLib

Gradle will build all flavors. If you’re experiencing problems with Android Studio, just sync the project after executing this command from command line.

Now you can deploy the application to a device or an emulator. Go to Gradle projects, expand :app module, expand Tasks, expand install and double click installDebug target.

We will discuss how to use further SDL2 libraries in next articles. You can find more under topic SDL2.

11. October 2016

Siriel 05 – Open source game engines

After working with Unity Editor I have realized that it has several drawbacks from my point of view.

  • Build time for HTML5 was extremely long even when the game was very small. It took several minutes to build the application.
  • Personal license always displays logo of Unity and I had to wait for the logo to fade out even when doing small iterations and testing of the game.
  • Unity is close source and even when I found the bug, Unity QA was not able to simulate it and they dropped the issue.

I started to seek for other engines and I was surprised by myriad of engines described at Wikipedia. The list is quite exhaustive and it is little bit hard to recognize the maturity of each project.

There is another list at GitHub which contains just open source engines. Projects are sorted by stars which makes it easier to see how is the project popular.

3. October 2016

Siriel 04 – #ifdef in Unity could lead into bad code maintainability

I was playing with Unity. Extending functionality bit by bit. Then I decided to make my game available also for mobile device.

So I searched for another tutorial from Unity – 2D Roguelike 14 of 14 : Mobile Controls. The tutorial seemed to be ok. But at one moment I froze in horror. The author was using #ifdef directly in high level code.

In my opinion this is very bad code smell. If you’re C expert and you’re playing with low-level API then you’ll need #ifdef, but this is high level code.

You may ask what is wrong about #ifdef in my “C# Script”. Well, here is very nice answer for C++.

#ifdef is something which should be treated with maximal caution, because it has tendency to explode into many Heisenbugs.

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