# Golem

`golem` is an opinionated mostly-safe graphics API

When possible, `golem` should make simple things safe (bind objects before acting on them, or
check if they're bound for objects that are expensive to bind.) However, when not possible or
convenient (bounds checking the indices in an element buffer, for example), `golem` provides
unsafe APIs with well-defined safety conditions.

A minimal example to display a triangle:

```rust
use golem::*;
use golem::Dimension::*;
fn func(ctx: &Context) -> Result<(), GolemError> {
 let vertices = [
     // Position         Color
     -0.5, -0.5,         1.0, 0.0, 0.0, 1.0,
     0.5, -0.5,          0.0, 1.0, 0.0, 1.0,
     0.0, 0.5,           0.0, 0.0, 1.0, 1.0
 ];
 let indices = [0, 1, 2];

 let mut shader = ShaderProgram::new(
     ctx,
     ShaderDescription {
         vertex_input: &[
             Attribute::new("vert_position", AttributeType::Vector(D2)),
             Attribute::new("vert_color", AttributeType::Vector(D4)),
         ],
         fragment_input: &[Attribute::new("frag_color", AttributeType::Vector(D4))],
         uniforms: &[],
         vertex_shader: r#" void main() {
         gl_Position = vec4(vert_position, 0, 1);
         frag_color = vert_color;
         }"#,
         fragment_shader: r#" void main() {
         gl_FragColor = frag_color;
         }"#,
     },
 )?;
 let mut vb= VertexBuffer::new(ctx)?;
 let mut eb  ElementBuffer::new(ctx)?;
 vb.set_data(&vertices);
 eb.set_data(&indices);
 shader.bind();
 ctx.clear();
 unsafe {
    shader.draw(&vb, &eb, 0..indices.len(), GeometryMode::Triangles)?;
 }
 Ok(())
}
```

The core type of `golem` is the `Context`, which is constructed from the `glow::Context`.
From the `Context`, `ShaderProgram`s are created, which take in data from `Buffer`s. Once
the data is uploaded to the GPU via `Buffer::set_data`, it can be drawn via `ShaderProgram::draw`.

## Initializing

The user is responsible for windowing and providing a valid glow Context to create a
`Context`. You can try out the [`blinds`](https://crates.io/crates/blinds) crate, which works
well with `golem`, but using `winit` directly or other windowing solutions like `sdl2` are also
options.

## OpenGL Versions
The backend is currently implemented via `glow`, and it targets OpenGL 3.2 on desktop and WebGL 1 (so it
should run on a wide range of hardware.) GL 3.2 is selected for maximum desktop availability,
and WebGL 1 is available on 97% of clients to WebGL's 75% (taken from caniuse.com at time of
writing.)

### GLSL
Shaders are partially generated by `golem` at runtime, to deal with platform incompatibilities. The user provides the main function for the shader, and `golem` supplies the version number, the shader inputs, outputs, and uniforms. See the `ShaderDescription` docs for more.