Capabilities API

Declared in include/metagl/Capabilities.hpp. After calling metagl::Initialize(), the Capabilities API lets you query which OpenGL ES and WebGL feature sets the current context supports.

Overview

meta-gl reads GL_VERSION, GL_VENDOR, GL_RENDERER, GL_SHADING_LANGUAGE_VERSION, and enumerates GL_EXTENSIONS during initialization. The results are cached in a Capabilities struct. You can read this struct at any time without making additional GL calls.

Capabilities Struct

struct Capabilities {
    std::string version_string;
    std::string vendor;
    std::string renderer;
    std::string shading_language_version;
    std::vector<std::string> extensions;

    bool gles20 = false;  // true for ES 2.0 or higher
    bool gles30 = false;  // true for ES 3.0 or higher
    bool gles31 = false;  // true for ES 3.1 or higher
    bool gles32 = false;  // true for ES 3.2 or higher

    // Only meaningful when compiled with Emscripten:
    bool webgl1 = false;
    bool webgl2 = false;
};

Note: Version flags are cumulative. If gles32 == true, then gles31, gles30, and gles20 are all also true.

Query Functions

Function	Returns	Description
`GetCapabilities()`	`const Capabilities&`	Full capabilities struct, valid after Initialize()
`SupportsGLES20()`	`bool`	True if context is ES 2.0+
`SupportsGLES30()`	`bool`	True if context is ES 3.0+
`SupportsGLES31()`	`bool`	True if context is ES 3.1+
`SupportsGLES32()`	`bool`	True if context is ES 3.2+
`SupportsWebGL2()`	`bool`	True when on WebGL 2 (Emscripten only)
`HasExtension(name)`	`bool`	True if the named extension is present

All functions are [[nodiscard]] and noexcept.

Extension Queries

// Check for a specific extension:
if (metagl::HasExtension("GL_EXT_texture_filter_anisotropic")) {
    // enable anisotropic filtering
}

// Iterate all extensions:
const auto& caps = metagl::GetCapabilities();
for (const auto& ext : caps.extensions) {
    std::cout << ext << "\n";
}

// Print driver info:
std::cout << "Vendor:   " << caps.vendor << "\n";
std::cout << "Renderer: " << caps.renderer << "\n";
std::cout << "Version:  " << caps.version_string << "\n";

Usage Patterns

Feature-gating at startup

metagl::Initialize(loader);

const auto& caps = metagl::GetCapabilities();
bool canCompute     = caps.gles31;
bool canGeomShader  = caps.gles32;
bool hasFloatTex    = caps.gles30 ||
    metagl::HasExtension("GL_OES_texture_float");

Adaptive quality

if (metagl::SupportsGLES30()) {
    useTexStorage();  // immutable storage, ES3+
} else {
    useTexImage();    // mutable storage, ES2
}

if (metagl::HasExtension("GL_EXT_texture_compression_s3tc")) {
    loadDXT1Textures();
} else if (metagl::SupportsGLES30()) {
    loadETC2Textures();  // required in ES3
} else {
    loadRGBATextures();  // fallback
}

OpenGL ES Version Matrix

ES version	Key new features	Flag
2.0	Vertex + fragment shaders, VBOs, textures, framebuffers (basic)	`gles20`
3.0	VAOs, UBOs, transform feedback, MSAA FBOs, ETC2/EAC textures, integer formats, 3D textures, instancing, sync objects, queries	`gles30`
3.1	Compute shaders, SSBOs, atomic counters, image load/store, indirect draw/dispatch, separate shader programs, vertex binding API	`gles31`
3.2	Geometry shaders, tessellation, ASTC textures, robust context, debug output, draw indirect with base vertex, layered FBOs	`gles32`