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OpenGL ES and input for iOS, tvOS, Android, and WebGL

brackeen
brackeen
pushedAt 1 month ago

brackeen/glfm

GLFM

Write OpenGL ES code in C/C++ without writing platform-specific code.

GLFM is an OpenGL ES layer for mobile devices and the web. GLFM supplies an OpenGL ES context and input events. It is largely inspired by GLFW.

GLFM is written in C and runs on iOS 9, tvOS 9, Android 4.1 (API 16), and WebGL 1.0 (via Emscripten).

Additionally, GLFM provides Metal support on iOS and tvOS.

Features

  • OpenGL ES 2, OpenGL ES 3, and Metal display setup.
  • Retina / high-DPI support.
  • Touch and keyboard events.
  • Accelerometer, magnetometer, gyroscope, and device rotation (iOS/Android only)
  • Events for application state and context loss.

Non-goals

GLFM is limited in scope, and isn't designed to provide everything needed for an app. For example, GLFM doesn't provide (and will never provide) the following:

  • No image loading.
  • No text rendering.
  • No audio.
  • No menus, UI toolkit, or scene graph.
  • No integration with other mobile features like web views, maps, or game scores.

Instead, GLFM can be used with other cross-platform libraries that provide what an app needs.

Use GLFM

A CMakeLists.txt file is provided for convenience, although CMake is not required.

Without CMake:

  1. Add the GLFM source files (in include and src) to your project.
  2. Include a void glfmMain(GLFMDisplay *display) function in a C/C++ file.

Example

This example initializes the display in glfmMain() and draws a triangle in onFrame(). A more detailed example is available here.

#include "glfm.h"
#include <string.h>

static GLint program = 0;
static GLuint vertexBuffer = 0;

static void onFrame(GLFMDisplay *display);
static void onSurfaceCreated(GLFMDisplay *display, int width, int height);
static void onSurfaceDestroyed(GLFMDisplay *display);

void glfmMain(GLFMDisplay *display) {
    glfmSetDisplayConfig(display,
                         GLFMRenderingAPIOpenGLES2,
                         GLFMColorFormatRGBA8888,
                         GLFMDepthFormatNone,
                         GLFMStencilFormatNone,
                         GLFMMultisampleNone);
    glfmSetSurfaceCreatedFunc(display, onSurfaceCreated);
    glfmSetSurfaceResizedFunc(display, onSurfaceCreated);
    glfmSetSurfaceDestroyedFunc(display, onSurfaceDestroyed);
    glfmSetRenderFunc(display, onFrame);
}

static void onSurfaceCreated(GLFMDisplay *display, int width, int height) {
    glViewport(0, 0, width, height);
}

static void onSurfaceDestroyed(GLFMDisplay *display) {
    // When the surface is destroyed, all existing GL resources are no longer valid.
    program = 0;
    vertexBuffer = 0;
}

static GLuint compileShader(const GLenum type, const GLchar *shaderString) {
    const GLint shaderLength = (GLint)strlen(shaderString);
    GLuint shader = glCreateShader(type);
    glShaderSource(shader, 1, &shaderString, &shaderLength);
    glCompileShader(shader);
    return shader;
}

static void onFrame(GLFMDisplay *display) {
    if (program == 0) {
        const GLchar *vertexShader =
            "attribute highp vec4 position;\n"
            "void main() {\n"
            "   gl_Position = position;\n"
            "}";

        const GLchar *fragmentShader =
            "void main() {\n"
            "  gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);\n"
            "}";

        program = glCreateProgram();
        GLuint vertShader = compileShader(GL_VERTEX_SHADER, vertexShader);
        GLuint fragShader = compileShader(GL_FRAGMENT_SHADER, fragmentShader);

        glAttachShader(program, vertShader);
        glAttachShader(program, fragShader);

        glLinkProgram(program);

        glDeleteShader(vertShader);
        glDeleteShader(fragShader);
    }
    if (vertexBuffer == 0) {
        const GLfloat vertices[] = {
             0.0,  0.5, 0.0,
            -0.5, -0.5, 0.0,
             0.5, -0.5, 0.0,
        };
        glGenBuffers(1, &vertexBuffer);
        glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
        glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    }

    glClearColor(0.4f, 0.0f, 0.6f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    glUseProgram(program);
    glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);

    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
    glDrawArrays(GL_TRIANGLES, 0, 3);
    
    glfmSwapBuffers(display);
}

API

See glfm.h

Build the GLFM examples with Xcode 12

Requires CMake 3.18.

mkdir -p build/ios && cd build/ios && cmake -DGLFM_BUILD_EXAMPLE=ON -G Xcode ../..
open GLFM.xcodeproj

Switch to the glfm_example target and run on the simulator or a device.

Build the GLFM examples with Emscripten

Tested with Emscripten 2.0.8.

Make sure EMSDK is set, and build:

mkdir -p build/emscripten && cd build/emscripten
cmake -DGLFM_BUILD_EXAMPLE=ON -DCMAKE_TOOLCHAIN_FILE=$EMSDK/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -DCMAKE_BUILD_TYPE=MinSizeRel ../..
cmake --build .

Then run locally:

emrun example/glfm_example.html

Build the GLFM examples with Android Studio 4

There is no CMake generator for Android Studio projects, but you can include CMakeLists.txt in a new or existing project.

  1. Select "Start a new Android Studio project".
  2. Select "No Activity".
  3. In "Save location", enter [path/to/glfm]/build/android and press "Finish".
  4. In AndroidManifest.xml, add the main <activity> like so:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          package="com.brackeen.glfmexample">

    <uses-feature android:glEsVersion="0x00020000" android:required="true" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true">

        <!-- Add this activity to your AndroidManifest.xml -->
        <activity android:name="android.app.NativeActivity"
                  android:configChanges="orientation|screenLayout|screenSize|keyboardHidden|keyboard">
            <meta-data
                android:name="android.app.lib_name"
                android:value="glfm_example" />  <!-- glfm_example, glfm_compass, or glfm_test_pattern -->
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>
    </application>

</manifest>
  1. In app/build.gradle, add the externalNativeBuild and sourceSets.main sections like so:
apply plugin: 'com.android.application'

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.2"
    defaultConfig {
        applicationId "com.brackeen.glfmexample"
        minSdkVersion 15
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"

        // Add externalNativeBuild in defaultConfig (1/2)
        externalNativeBuild {
            cmake {
                arguments "-DGLFM_BUILD_EXAMPLE=ON"
            }
        }
    }
    
    // Add sourceSets.main and externalNativeBuild (2/2)
    sourceSets.main {
        assets.srcDirs = ["../../../example/assets"]
    }
    externalNativeBuild {
        cmake {
            path "../../../CMakeLists.txt"
        }
    }
}
  1. Press "Sync Now" and "Run 'app'"

Caveats

  • OpenGL ES 3.1 and 3.2 support is only available in Android.
  • GLFM is not thread-safe. All GLFM functions must be called on the main thread (that is, from glfmMain or from the callback functions).
  • On iOS, character input works great, but keyboard events are not ideal. Using the keyboard (on an iOS device via Bluetooth keyboard or on the simulator via a Mac's keyboard), only a few keys are detected (arrows keys and the escape key), and key release events are not reported.
  • On Android, keyboard events work great, but character events are not ideal. Some special characters, like emoji characters, will not work. This is due to an issue in the NDK.
  • Orientation lock probably doesn't work on HTML5.

Questions

What IDE should I use? Why is there no desktop implementation? Use Xcode or Android Studio. For desktop, use GLFW with the IDE of your choice.

If you prefer not using the mobile simulators for everyday development, a good solution is to use GLFW instead, and then later port your app to GLFM. Not all OpenGL calls will port to OpenGL ES perfectly, but for maximum OpenGL portability, use OpenGL 3.2 Core Profile on desktop and OpenGL ES 2.0 on mobile.

Moving forward, GLFM APIs will look more like GLFW's, so porting will get easier as GLFM development continues.

Why is the entry point glfmMain() and not main()?

Otherwise, it wouldn't work on iOS. To initialize the Objective-C environment, the main() function must create an autorelease pool and call the UIApplicationMain() function, which never returns. On iOS, GLFM doesn't call glfmMain() until after the UIApplicationDelegate and UIViewController are initialized.

Why is GLFM event-driven? Why does GLFM take over the main loop?

Otherwise, it wouldn't work on iOS (see above) or on HTML5, which is event-driven.

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