OpenGL ES

Android includes support for high performance 2D and 3D graphics with the Open Graphics Library
(OpenGL®), specifically, the OpenGL ES API. OpenGL is a cross-platform graphics API that
specifies a
standard software interface for 3D graphics processing hardware. OpenGL ES is a flavor of the OpenGL
specification intended for embedded devices. Android supports several versions of the OpenGL ES
API:

OpenGL ES 1.0 and 1.1 - This API specification is supported by Android 1.0 and higher.

Caution:
Support of the OpenGL ES 3.0 API on a device requires an implementation of this graphics
pipeline provided by the device manufacturer. A device running Android 4.3 or higher may
not support the OpenGL ES 3.0 API. For information on checking what version of OpenGL ES
is supported at run time, see Checking OpenGL ES version.

Note:
The specific API provided by the Android framework is similar to the J2ME JSR239 OpenGL ES API,
but is not identical. If you are familiar with J2ME JSR239 specification, be alert for
variations.

The basics

Android supports OpenGL both through its framework API and the Native Development
Kit (NDK). This topic focuses on the Android framework interfaces. For more information about the
NDK, see the Android NDK.

There are two foundational classes in the Android framework that let you create and manipulate
graphics with the OpenGL ES API: GLSurfaceView and
GLSurfaceView.Renderer. If your goal is to use OpenGL in your Android application,
understanding how to implement these classes in an activity should be your first objective.

This class is a View where you can draw and manipulate objects using
OpenGL API calls and is similar in function to a SurfaceView. You can use
this class by creating an instance of GLSurfaceView and adding your
Renderer to it. However, if you want to capture
touch screen events, you should extend the GLSurfaceView class to
implement the touch listeners, as shown in OpenGL training lesson,
Responding to touch events.

onSurfaceCreated(): The system calls this
method once, when creating the GLSurfaceView. Use this method to perform
actions that need to happen only once, such as setting OpenGL environment parameters or
initializing OpenGL graphic objects.

onDrawFrame(): The system calls this method on each redraw of the GLSurfaceView. Use this method as the primary execution point for
drawing (and re-drawing) graphic objects.

onSurfaceChanged(): The system calls this method when the GLSurfaceView geometry changes, including changes in size of the GLSurfaceView or orientation of the device screen. For example, the system calls
this method when the device changes from portrait to landscape orientation. Use this method to
respond to changes in the GLSurfaceView container.

android.opengl.GLES20 - This package provides the
interface to OpenGL ES 2.0 and is available starting with Android 2.2 (API level 8).

OpenGL ES 3.0/3.1 API Packages

android.opengl - This package provides the interface to the OpenGL ES 3.0/3.1
classes.
Version 3.0 is available starting with Android 4.3 (API level 18). Version 3.1 is available
starting with Android 5.0 (API level 21).

Declaring OpenGL requirements

If your application uses OpenGL features that are not available on all devices, you must include
these requirements in your AndroidManifest.xml
file. Here are the most common OpenGL manifest declarations:

OpenGL ES version requirements - If your application requires a specific
version of
OpenGL ES, you must declare that requirement by adding the following settings to your manifest as
shown below.

Adding this declaration causes Google Play to restrict your application from being
installed on devices that do not support OpenGL ES 2.0. If your application is exclusively for
devices that support OpenGL ES 3.0, you can also specify this in your manifest:

Note:
The OpenGL ES 3.x API is backwards-compatible with the 2.0 API, which means you can be more
flexible with your implementation of OpenGL ES in your application. By declaring the OpenGL
ES 2.0 API as a requirement in your manifest, you can use that API version as a default, check
for the availability of the 3.x API at run time and then use OpenGL ES 3.x features if the
device supports it. For more information about checking the OpenGL ES version supported by a
device, see Checking OpenGL ES version.

Declaring texture compression requirements in your manifest hides your application from users
with devices that do not support at least one of your declared compression types. For more
information on how Google Play filtering works for texture compressions, see the
Google Play and texture compression filtering section of the <supports-gl-texture> documentation.

Mapping coordinates for drawn objects

One of the basic problems in displaying graphics on Android devices is that their screens can
vary in size and shape. OpenGL assumes a square, uniform coordinate system and, by default, happily
draws those coordinates onto your typically non-square screen as if it is perfectly square.

The illustration above shows the uniform coordinate system assumed for an OpenGL frame on the
left, and how these coordinates actually map to a typical device screen in landscape orientation
on the right. To solve this problem, you can apply OpenGL projection modes and camera views to
transform coordinates so your graphic objects have the correct proportions on any display.

In order to apply projection and camera views, you create a projection matrix and a camera view
matrix and apply them to the OpenGL rendering pipeline. The projection matrix recalculates the
coordinates of your graphics so that they map correctly to Android device screens. The camera view
matrix creates a transformation that renders objects from a specific eye position.

Projection and camera view in OpenGL ES 1.0

In the ES 1.0 API, you apply projection and camera view by creating each matrix and then
adding them to the OpenGL environment.

Projection matrix - Create a projection matrix using the geometry of the
device screen in order to recalculate object coordinates so they are drawn with correct proportions.
The following example code demonstrates how to modify the onSurfaceChanged() method of a GLSurfaceView.Renderer
implementation to create a projection matrix based on the screen's aspect ratio and apply it to the
OpenGL rendering environment.

Camera transformation matrix - Once you have adjusted the coordinate system
using a projection matrix, you must also apply a camera view. The following example code shows how
to modify the onDrawFrame() method of a GLSurfaceView.Renderer
implementation to apply a model view and use the
GLU.gluLookAt() utility to create a viewing tranformation
which simulates a camera position.

Projection and camera view in OpenGL ES 2.0 and higher

In the ES 2.0 and 3.0 APIs, you apply projection and camera view by first adding a matrix member
to the vertex shaders of your graphics objects. With this matrix member added, you can then
generate and apply projection and camera viewing matrices to your objects.

Add matrix to vertex shaders - Create a variable for the view projection matrix
and include it as a multiplier of the shader's position. In the following example vertex shader
code, the included uMVPMatrix member allows you to apply projection and camera viewing
matrices to the coordinates of objects that use this shader.

Kotlin

private val vertexShaderCode =
// This matrix member variable provides a hook to manipulate
// the coordinates of objects that use this vertex shader.
"uniform mat4 uMVPMatrix; \n" +
"attribute vec4 vPosition; \n" +
"void main(){ \n" +
// The matrix must be included as part of gl_Position
// Note that the uMVPMatrix factor *must be first* in order
// for the matrix multiplication product to be correct.
" gl_Position = uMVPMatrix * vPosition; \n" +
"} \n"

Java

private final String vertexShaderCode =
// This matrix member variable provides a hook to manipulate
// the coordinates of objects that use this vertex shader.
"uniform mat4 uMVPMatrix; \n" +
"attribute vec4 vPosition; \n" +
"void main(){ \n" +
// The matrix must be included as part of gl_Position
// Note that the uMVPMatrix factor *must be first* in order
// for the matrix multiplication product to be correct.
" gl_Position = uMVPMatrix * vPosition; \n" +
"} \n";

Note: The example above defines a single transformation matrix
member in the vertex shader into which you apply a combined projection matrix and camera view
matrix. Depending on your application requirements, you may want to define separate projection
matrix and camera viewing matrix members in your vertex shaders so you can change them
independently.

Access the shader matrix - After creating a hook in your vertex shaders to
apply projection and camera view, you can then access that variable to apply projection and
camera viewing matrices. The following code shows how to modify the onSurfaceCreated() method of a GLSurfaceView.Renderer implementation to access the matrix
variable defined in the vertex shader above.

Java

Create projection and camera viewing matrices - Generate the projection and
viewing matrices to be applied the graphic objects. The following example code shows how to modify
the onSurfaceCreated() and
onSurfaceChanged() methods of a
GLSurfaceView.Renderer implementation to create camera view matrix and a
projection matrix based on the screen aspect ratio of the device.

Apply projection and camera viewing matrices - To apply the projection and
camera view transformations, multiply the matrices together and then set them into the vertex
shader. The following example code shows how modify the onDrawFrame() method of a GLSurfaceView.Renderer implementation to combine
the projection matrix and camera view created in the code above and then apply it to the graphic
objects to be rendered by OpenGL.

Shape faces and winding

In OpenGL, the face of a shape is a surface defined by three or more points in three-dimensional
space. A set of three or more three-dimensional points (called vertices in OpenGL) have a front face
and a back face. How do you know which face is front and which is the back? Good question. The
answer has to do with winding, or, the direction in which you define the points of a shape.

Figure 1. Illustration of a coordinate list which translates into a
counterclockwise drawing order.

In this example, the points of the triangle are defined in an order such that they are drawn in a
counterclockwise direction. The order in which these coordinates are drawn defines the winding
direction for the shape. By default, in OpenGL, the face which is drawn counterclockwise is the
front face. The triangle shown in Figure 1 is defined so that you are looking at the front face of
the shape (as interpreted by OpenGL) and the other side is the back face.

Why is it important to know which face of a shape is the front face? The answer has to do with a
commonly used feature of OpenGL, called face culling. Face culling is an option for the OpenGL
environment which allows the rendering pipeline to ignore (not calculate or draw) the back face of a
shape, saving time, memory and processing cycles:

Java

If you try to use the face culling feature without knowing which sides of your shapes are the
front and back, your OpenGL graphics are going to look a bit thin, or possibly not show up at all.
So, always define the coordinates of your OpenGL shapes in a counterclockwise drawing order.

Note: It is possible to set an OpenGL environment to treat the
clockwise face as the front face, but doing so requires more code and is likely to confuse
experienced OpenGL developers when you ask them for help. So don’t do that.

OpenGL versions and device compatibility

The OpenGL ES 1.0 and 1.1 API specifications have been supported since Android 1.0.
Beginning with Android 2.2 (API level 8), the framework supports the OpenGL ES 2.0 API
specification. OpenGL ES 2.0 is supported by most Android devices and is recommended for new
applications being developed with OpenGL. OpenGL ES 3.0 is supported with Android 4.3
(API level 18) and higher, on devices that provide an implementation of the OpenGL ES 3.0 API.
For information about the relative number of Android-powered devices
that support a given version of OpenGL ES, see the
OpenGL ES version dashboard.

Graphics programming with OpenGL ES 1.0/1.1 API is significantly different than using the 2.0
and higher versions. The 1.x version of the API has more convenience methods and a fixed graphics
pipeline, while the OpenGL ES 2.0 and 3.0 APIs provide more direct control of the pipeline through
use of OpenGL shaders. You should carefully consider the graphics requirements and choose the API
version that works best for your application. For more information, see
Choosing an OpenGL API version.

The OpenGL ES 3.0 API provides additional features and better performance than the 2.0 API and is
also backward compatible. This means that you can potentially write your application targeting
OpenGL ES 2.0 and conditionally include OpenGL ES 3.0 graphics features if they are available. For
more information on checking for availability of the 3.0 API, see
Checking OpenGL ES version

Texture compression support

Texture compression can significantly increase the performance of your OpenGL application by
reducing memory requirements and making more efficient use of memory bandwidth. The Android
framework provides support for the ETC1 compression format as a standard feature, including a
ETC1Util utility class and the etc1tool compression tool (located in the
Android SDK at <sdk>/tools/). For an example of an Android application that uses
texture compression, see the CompressedTextureActivity code sample in Android SDK
(<sdk>/samples/<version>/ApiDemos/src/com/example/android/apis/graphics/).

Caution: The ETC1 format is supported by most Android devices,
but is not guaranteed to be available. To check if the ETC1 format is supported on a device, call
the ETC1Util.isETC1Supported() method.

Note: The ETC1 texture compression format does not support textures with a
transparency (alpha channel). If your application requires textures with transparency, you should
investigate other texture compression formats available on your target devices.

The ETC2/EAC texture compression formats are guaranteed to be available when using the OpenGL ES
3.0 API. This texture format offers excellent compression ratios with high visual quality and the
format also supports transparency (alpha channel).

Beyond the ETC formats, Android devices have varied support for texture compression based on
their GPU chipsets and OpenGL implementations. You should investigate texture compression support on
the devices you are are targeting to determine what compression types your application should
support. In order to determine what texture formats are supported on a given device, you must
query the device and review the OpenGL extension names,
which identify what texture compression formats (and other OpenGL features) are supported by the
device. Some commonly supported texture compression formats are as follows:

ATITC (ATC) - ATI texture compression (ATITC or ATC) is available on a
wide variety of devices and supports fixed rate compression for RGB textures with and without
an alpha channel. This format may be represented by several OpenGL extension names, for example:

GL_AMD_compressed_ATC_texture

GL_ATI_texture_compression_atitc

PVRTC - PowerVR texture compression (PVRTC) is available on a wide
variety of devices and supports 2-bit and 4-bit per pixel textures with or without an alpha channel.
This format is represented by the following OpenGL extension name:

GL_IMG_texture_compression_pvrtc

S3TC (DXTn/DXTC) - S3 texture compression (S3TC) has several
format variations (DXT1 to DXT5) and is less widely available. The format supports RGB textures with
4-bit alpha or 8-bit alpha channels. These formats are represented by the following OpenGL extension
name:

GL_EXT_texture_compression_s3tc

Some devices only support the DXT1 format variation; this limited support is represented by the
following OpenGL extension name:

GL_EXT_texture_compression_dxt1

3DC - 3DC texture compression (3DC) is a less widely available format that
supports RGB textures with an alpha channel. This format is represented by the following OpenGL
extension name:

GL_AMD_compressed_3DC_texture

Warning: These texture compression formats are not
supported on all devices. Support for these formats can vary by manufacturer and device. For
information on how to determine what texture compression formats are on a particular device, see
the next section.

Note: Once you decide which texture compression formats your
application will support, make sure you declare them in your manifest using
<supports-gl-texture>
. Using this declaration enables filtering by external services such as Google Play, so that
your app is installed only on devices that support the formats your app requires. For details, see
OpenGL manifest declarations.

Determining OpenGL extensions

Implementations of OpenGL vary by Android device in terms of the extensions to the OpenGL ES API
that are supported. These extensions include texture compressions, but typically also include other
extensions to the OpenGL feature set.

To determine what texture compression formats, and other OpenGL extensions, are supported on a
particular device:

Run the following code on your target devices to determine what texture compression
formats are supported:

Kotlin

var extensions = gl.glGetString(GL10.GL_EXTENSIONS)

Java

String extensions = gl.glGetString(GL10.GL_EXTENSIONS);

Warning: The results of this call vary by device model! You
must run this call on several target devices to determine what compression types are commonly
supported.

Review the output of this method to determine what OpenGL extensions are supported on the
device.

Android Extension Pack (AEP)

The AEP ensures that your application supports a standardized set of OpenGL extensions above
and beyond
the core set described in the OpenGL 3.1 specification. Packaging these extensions together
encourages a consistent set of functionality across devices, while allowing developers to take full
advantage of the latest crop of mobile GPU devices.

The AEP also improves support for images, shader storage buffers, and atomic counters in
fragment shaders.

For your app to be able to use the AEP, the app's manifest must declare that the AEP is required.
In addition, the platform version must support it.

Checking the OpenGL ES version

There are several versions of OpenGL ES available on Android devices. You can specify the
minimum version of the API your application requires in your manifest, but
you may also want to take advantage of features in a newer API at the same time. For example,
the OpenGL ES 3.0 API is backward-compatible with the 2.0 version of the API, so you may want to
write your application so that it uses OpenGL ES 3.0 features, but falls back to the 2.0 API if the
3.0 API is not available.

Before using OpenGL ES features from a version higher than the minimum required in your
application manifest, your application should check the version of the API available on the device.
You can do this in one of two ways:

Attempt to create the higher-level OpenGL ES context (EGLContext) and
check the result.

Create a minimum-supported OpenGL ES context and check the version value.

The following example code demonstrates how to check the available OpenGL ES version by creating
an EGLContext and checking the result. This example shows how to check for
OpenGL ES 3.0 version:

With this approach, if you discover that the device supports a higher-level API version, you
must destroy the minimum OpenGL ES context and create a new context with the higher
available API version.

Choosing an OpenGL API version

OpenGL ES 1.0 API version (and the 1.1 extensions), version 2.0, and version 3.0 all provide high
performance graphics interfaces for creating 3D games, visualizations and user interfaces. Graphics
progamming for OpenGL ES 2.0 and 3.0 is largely similar, with version 3.0 representing a superset
of the 2.0 API with additional features. Programming for the OpenGL ES 1.0/1.1 API versus OpenGL ES
2.0 and 3.0 differs significantly, and so developers should carefully consider the following
factors before starting development with these APIs:

Performance - In general, OpenGL ES 2.0 and 3.0 provide faster graphics
performance than the ES 1.0/1.1 APIs. However, the performance difference can vary depending on
the Android device your OpenGL application is running on, due to differences in hardware
manufacturer's implementation of the OpenGL ES graphics pipeline.

Device Compatibility - Developers should consider the types of devices,
Android versions and the OpenGL ES versions available to their customers. For more information
on OpenGL compatibility across devices, see the OpenGL versions and
device compatibility section.

Coding Convenience - The OpenGL ES 1.0/1.1 API provides a fixed function
pipeline and convenience functions which are not available in the OpenGL ES 2.0 or 3.0 APIs.
Developers who are new to OpenGL ES may find coding for version 1.0/1.1 faster and more
convenient.

Graphics Control - The OpenGL ES 2.0 and 3.0 APIs provide a higher degree
of control by providing a fully programmable pipeline through the use of shaders. With more
direct control of the graphics processing pipeline, developers can create effects that would be
very difficult to generate using the 1.0/1.1 API.

Texture Support - The OpenGL ES 3.0 API has the best support for texture
compression because it guarantees availability of the ETC2 compression format, which supports
transparency. The 1.x and 2.0 API implementations usually include support for ETC1, however
this texture format does not support transparency and so you must typically provide resources
in other compression formats supported by the devices you are targeting. For more information,
see Texture compression support.

While performance, compatibility, convenience, control and other factors may influence your
decision, you should pick an OpenGL API version based on what you think provides the best experience
for your users.

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