13. September 2017

SDL2_mixer for Android playing WAV file

In previous articles, we were talking about PNG and JPEG support in SDL2 for Android. Let’s add some sounds to our application.

The initial steps are same as in case of SDL2_image.

Register library in settings.gradle:

include ':SDL2_mixer'

The library should be stored in SDL2_mixer directory with build.gradle that written in style for a library.

Now update our C application.

First of all, it is necessary to initialize the library. Then it is possible to load the sound file.

    if (Mix_OpenAudio(22050, MIX_DEFAULT_FORMAT, 2, 4096) == -1 ) {
        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
                     "Couldn't open mixer: %s", SDL_GetError());
        return 2;
    }
    Mix_Chunk *sample = Mix_LoadWAV("cuckoo.wav");
    if (sample == NULL) {
        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, 
                     "Unable to load wave file\n");
        return 3;
    }

The file WAV should be stored in app/src/main/assets. Just small reminder: this is just a virtual directory, and you won’t be able to access it from other application on Android.

Playing the sound is simple:

Mix_PlayChannel(-1, sample, 0);

The last important thing about SDL2_mixer is that you should close SDL2_mixer when exiting the main. Otherwise, when you relaunch SDLActivity, it won’t be able to play any sound.

Mix_CloseAudio();

You can find the source code at GitHub in sdl2-android-example repository. Further articles about SDL2 and android are available under the tag SDL2.

11. September 2017

How to increase font size in Wireshark 2.4 on Windows

Wireshark is based on the new version of QT, and it has a similar problem on Windows like pgAdmin 4.

If you have a screen with higher density, the font will be too small.

The solution is to add one parameter for QT engine to handle DPI differently.

Open PowerShell as Administrator and go to the directory with Wireshark open qt.conf file:

cd "C:\Program Files\Wireshark"
notepad qt.conf

Write there following content:

[Platforms]
WindowsArguments = dpiawareness=0

Save the file and start Wireshark.

Note: make sure that the file name is just qt.conf. Notepad could add .txt file extension when saving the file directly from Notepad.

Enjoy bigger font:

7. September 2017

Gradle Experimental Plugin Android error: Cannot invoke method dependencies()

Update: Engineers at Google fixed the issue. Thank you.

After initial setup of SDL2 application for Android, I decided to add one activity before launching SDL. So I created the new MainActivity which should launch SDLActivity after a tap on the button.

This time Gradle Experimental Plugin gave me a very fancy error: Cannot invoke method dependencies() on null object.

As always the error message does not provide too many hints how to solve the issue.

Android Studio automatically just appended a dependency into the Gradle file during creation of new MainActivity. So the code in build.gradle looked like this:

tasks.whenTaskAdded { task ->
    if (task.name.contains('compile')) {
        task.dependsOn ':main:distributeLib'
    }
}dependencies {
    compile 'com.android.support.constraint:constraint-layout:+'
}

Little bit weird code for dependencies. The solution was just to add a new line.

tasks.whenTaskAdded { task ->
    if (task.name.contains('compile')) {
        task.dependsOn ':main:distributeLib'
    }
}

dependencies {
    compile 'com.android.support.constraint:constraint-layout:+'
}

The whole project is available at github.com/georgik/sdl2-android-example project.

More articles about SDL2 for Android are available under tag sdl2.

3. September 2017

Difference between libraries and main Android application based on SDL2 built by Gradle 4

Gradle Android Experimental Plugin works without problem with Android Studio and it is the recommended approach use it when starting a new project with NDK.

It’s very easy to get started, but there are some traps. Let’s explore common mistake when writing Gradle build script for Android with NDK.

In case of an application which is based on C libraries, the goal is clear. Build libraries and then link everything into the final project.

The tricky part is the definition of dependencies. The definition for the main and for libraries is different. If you use the same style of definition you may run into error like: Android Studio is not able to import the project, because of missing .so file.

Here is the definition which you can find in build.gradle for the main module:

model {
     repositories {
        libs(PrebuiltLibraries) {
            SDL2 {
                headers.srcDir "../SDL2/include"
                binaries.withType(SharedLibraryBinary) {
                    sharedLibraryFile = file("${gradle.libDistributionRoot}/SDL2/lib/${targetPlatform.getName()}/libSDL2.so")
                }
            }
            SDL2_image {
                headers.srcDir "../SDL2_image/include"
                binaries.withType(SharedLibraryBinary) {
                    sharedLibraryFile = file("${gradle.libDistributionRoot}/SDL2_image/lib/${targetPlatform.getName()}/libSDL2_image.so")
                }
            }

        }
    }

   android {
        compileSdkVersion = gradle.sdkVersion
        buildToolsVersion = '25.0.3'

        defaultConfig {
            minSdkVersion.apiLevel = 13
            versionCode = 1
            versionName = '1.0'
        }
        ndk {
            moduleName = 'main'
            cppFlags.addAll([
                    "-I" + file("../SDL2/include/").absolutePath,
                    "-I" + file("../SDL2_image/include/").absolutePath,
            ])
            CFlags.addAll([
                    "-I" + file("../SDL2/include/").absolutePath,
                    "-I" + file("../SDL2_image/include/").absolutePath,
            ])
            stl "stlport_static"
        }

        sources {
            main {
                jni {
                    dependencies {
                        library 'SDL2' linkage 'shared'
                        library 'SDL2_jpeg' linkage 'shared'
                        library 'SDL2_png' linkage 'shared'
                        library 'SDL2_image' linkage 'shared'
                    }
                    source {
                        srcDirs 'src/'
                    }
                }
            }
        }

    }
}

If you look close enough, you’ll see that the first part of the file contains a definition of PrebuiltLibraries. These libraries are referencing directly the .so file. In the section dependencies, you can find reference to the declared dependencies.

Gradle will just build the app and it will grab all referenced .so files and put them into a final application. That is correct for the main module. When you’re writing build files for libraries, you should take a different approach.

Here is an example of SDL2_image/build.gradle file:

apply plugin: 'com.android.model.native'

model {

    android {
        compileSdkVersion = gradle.sdkVersion
        buildToolsVersion = '25.0.3'

        defaultConfig {
            minSdkVersion.apiLevel = 13
            versionCode = 1
            versionName = '1.0'
        }
        ndk {
            moduleName = 'SDL2_image'
            ldLibs.addAll(["GLESv1_CM", "EGL", "GLESv2", "log", "android", "dl"])
            CFlags.addAll(["-DGL_GLEXT_PROTOTYPES"])
            CFlags.addAll(["-I" + file("include/").absolutePath,
                           "-DGL_GLEXT_PROTOTYPES",
                           "-DLOAD_JPG",
                           "-DLOAD_PNG",
                           "-DLOAD_XPM"
            ])
        }

        sources {
            main {
                jni {
                    dependencies {
                        project ':SDL2' linkage 'shared'
                        project ':SDL2_jpeg' linkage 'shared'
                        project ':SDL2_png' linkage 'shared'
                    }
                    exportedHeaders {
                        srcDir "../SDL2/include"
                        srcDir "../SDL2_jpeg/include"
                        srcDir "../SDL2_png/include"
                    }
                    source {
                        srcDir "src"

                    }
                }
            }
        }

    }
}

Here you can see that there is no definition of PrebuiltLibraries, but the sources contain dependencies on projects of other libraries. In addition to that, there is exportedHeaders declaration which will tell the compiler where to find .h files. That is because you do not need any reference to .so dependencies when building .so library. You need just headers.

The different is very small in the dependencies section. It can simplify your build process if you use it correctly.

Here is an example of an error that occurs when the .so file is missing and library is referencing the file:

project refresh failed Error:Exception thrown while executing model rule: 
NdkComponentModelPlugin.Rules#createNativeBuildModel(NativeBuildConfig, ModelMap<androidbinaryinternal>, ModelMap<ndkabioptions>, NdkHandler) > create...

You can fix either build files or you can build missing libraries one by one.

The correct version of build files is available in sdl2-android-example project.

1. September 2017

SDL2 for Android API level 19

SDL2 example application works without problem with newer Androids API 21+. The problem was with API level 19. It took me some time to figure out reasons for very interesting errors.

Let’s examine error messages and investigate how to fix them.

When I’ve started sdl2-android-example on a device with API 19, it failed with error message: dlopen failed: cannot locate symbol “signal” referenced by libSDL2.so”

The root cause is not that obvious from the error message. It failed because the application has been built for API 21 instead of API 19.

The fixture is easy, just set sdkVersion to 19.

For this purpose, I’ve extracted sdkVersion to settings.gradle which can be found in the root directory of the project.

gradle.ext.sdkVersion = 19

Each module then has reference to this value:

model {
    android {
        compileSdkVersion = gradle.sdkVersion
...

Make complete clean and distributeLib to rebuild for proper API.

gradle clean dL

Hooray! Fixed. Let’s start the application.

Yey. New error: dlopen failed: could not load library “libSDL2_image.so” needed by “libmain.so”; caused by cannot locate symbol “png_set_longjmp_fn” referenced by “libSDL2_image.so”

The root cause of this issue is similar to the problem with JPEG described in the previous article. Paul Asiimwe found out that there is another library the name png and it has a different version so the application crashes.

To fix this issue it was necessary to rename whole png submodule to SDL2_png. Renaming requires clean and new distributeLib:

gradle clean dL

After these small tricks, the sdl2-android-example works even with API level 19.

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