OpenGL ES

Cheerp provides a GLES2 implementation based on WebGL which is designed to jump-start porting an existing GLES application/game to the browser.

genericjs only

Like all browser APIs, GLES is supported in genericjs code only.

Usage

The GLES2 API is declared in the GLES2/gl2.h header file, while webGLES specific methods are declared in the GLES2/webgles.h header. webGLES needs to be initialized using the following function

void webGLESInit(const client::String& canvasName);

which accept as the only argument the name of an existing HTML5 canvas element which should already exists at the time of webGLES initialization. An example HTML tag for such canvas:

<canvas width="1024" height="768" id="glcanvas"></canvas>

Raw WebGL access

webGLESInit creates a globally accessible WebGL context, you are free to use such context and you can mix and match between GLES and WebGL APIs. The context object is called webGLES and is accessible by including the GLES2/webgles.h header. For example:

#include <GLES2/webgles.h>
...
webGLES->createShader(GL_VERTEX_SHADER);

Helpers methods are available to convert GLES2 resources id to resource objects as used by WebGL:

client::WebGLProgram* webGLESLookupWebGLProgram(int objId);
client::WebGLShader* webGLESLookupWebGLShader(int objId);
client::WebGLBuffer* webGLESLookupWebGLBuffer(int objId);
client::WebGLFramebuffer* webGLESLookupWebGLFramebuffer(int objId);
client::WebGLRenderbuffer* webGLESLookupWebGLRenderbuffer(int objId);
client::WebGLTexture* webGLESLookupWebGLTexture(int objId);
client::WebGLUniformLocation* webGLESLookupWebGLUniformLocation(int objId);

Although webGLES implement the glTexImage2D API to load texture data, we only intend it to be used for data which is generated at run-time, like procedurally generated textures. We strongly advise using the WebGL provided texImage2D to load image data in JPEG or PNG format since the browser can decompress the images natively.

Passing data to WebGL uniform* APIs

uniform* APIs and, more in general, WebGL APIs which expect buffers require typed arrays of a suitable type.

If you have data stored in a C/C++ array or std::vector or any other contiguous memory storage, you can use cheerp::MakeTypedArray to convert the data into a JS typed array object. Please note that the conversion happens without copying, so it’s very efficient.