glow

To run the hello example on native platforms, use cargo run with the appropriate feature flag for your windowing backend:

• For glutin and winit: cargo run --features=glutin_winit
• For sdl2: cargo run --features=sdl2

To target web environments using web-sys, build the project using the wasm32-unknown-unknown target.

# web-sys
cargo build --target wasm32-unknown-unknown

To build glow for your current native operating system, use the standard cargo build command.

# native
cargo build

To build the hello example for the web using the wasm32-unknown-unknown target, follow these steps:

1. Navigate to the example directory: cd examples/hello.
2. Ensure your wasm-bindgen-cli version matches the version in Cargo.lock by installing it via cargo install wasm-bindgen-cli --version <version-from-Cargo.lock>.
3. Build the target: cargo build --target wasm32-unknown-unknown.
4. Generate the web assets using wasm-bindgen and move the index.html into the output directory.

Note: The wasm-bindgen command expects the path to the .wasm file relative to your current location in the examples/hello directory.

cd examples/hello
cargo build --target wasm32-unknown-unknown
mkdir -p generated
wasm-bindgen ../../target/wasm32-unknown-unknown/debug/hello.wasm --out-dir generated --target web
cp index.html generated

The following types are associated with a Context implementing HasContext. They represent the primary handles used in graphics programming:

• Shader: Handle to a shader object.
• Program: Handle to a shader program.
• Buffer: Handle to a buffer object.
• VertexArray: Handle to a vertex array object (VAO).
• Texture: Handle to a texture object.
• Sampler: Handle to a sampler object.
• Fence: Handle to a sync object/fence.
• Framebuffer: Handle to a framebuffer object.
• Renderbuffer: Handle to a renderbuffer object.
• Query: Handle to a query object.
• UniformLocation: Handle to a uniform location within a program.
• TransformFeedback: Handle to a transform feedback object.

The HasContext trait is the core abstraction in glow. It allows the library to provide a unified API for different graphics backends (like native OpenGL or WebGL via web-sys).

Any type implementing HasContext acts as a provider for OpenGL functions and manages the lifecycle of various graphics objects. The trait uses associated types to define what specific types represent shaders, programs, buffers, etc., for that particular context.

Safety Warning: All GL API usage must be valid according to the relevant GL specification. glow does not enforce these rules; the caller is responsible for ensuring that the context is valid and that calls follow the specification for the specific backend being used.

When performing texture operations like get_tex_image, glow uses enums to specify how pixel data is provided or received:

• PixelPackData<'a>: Used when sending data to the GPU (e.g., BufferOffset(u32) or Slice(Option<&'a mut [u8]>)).
• PixelUnpackData<'a>: Used when receiving data from the GPU (e.g., BufferOffset(u32) or Slice(Option<&'a [u8]>)).
• CompressedPixelUnpackData<'a>: Specifically for compressed data, using BufferRange(core::ops::Range<u32>) or Slice(&'a [u8]).

The tex_sub_image_2d and tex_sub_image_3d methods allow updating parts of textures. The behavior depends on the PixelUnpackData provided:

2D Sub-Image (tex_sub_image_2d)

• WebGL 1: Supports PixelUnpackData::Slice. Using PixelUnpackData::BufferOffset is not supported and will panic!.
• WebGL 2: Supports both PixelUnpackData::Slice and PixelUnpackData::BufferOffset.

3D Sub-Image (tex_sub_image_3d)

• WebGL 1: Not supported (will panic!).
• WebGL 2: Supports both PixelUnpackData::Slice and PixelUnpackData::BufferOffset.

Compressed Sub-Image (compressed_tex_sub_image_2d/3d)

• WebGL 1: Supports CompressedPixelUnpackData::Slice. Using CompressedPixelUnpackData::BufferRange is not supported and will panic!.
• WebGL 2: Supports both CompressedPixelUnpackData::Slice and CompressedPixelUnpackData::BufferRange.

The native backend uses specific wrapper types to represent OpenGL objects. These types ensure type safety when interacting with the Context. Common types include:

• NativeShader
• NativeProgram
• NativeBuffer
• NativeVertexArray
• NativeTexture
• NativeSampler
• NativeFence
• NativeFramebuffer
• NativeRenderbuffer
• NativeQuery
• NativeUniformLocation
• NativeTransformFeedback

The following operations are WebGL2 only. Attempting to call them while using a WebGL1 context will result in a panic:

• tex_image_3d_with_image_bitmap
• tex_image_3d_with_html_canvas_element
• tex_image_3d_with_html_image_element
• tex_image_3d_with_html_video_element
• tex_image_3d_with_video_frame
• tex_image_3d_with_image_data
• tex_sub_image_3d_with_image_bitmap
• tex_sub_image_3d_with_html_canvas_element
• tex_sub_image_3d_with_html_image_element
• tex_sub_image_3d_with_html_video_element
• tex_sub_image_3d_with_video_frame
• tex_sub_image_3d_with_image_data