pixset_derive 0.0.5

Macros 1.1 implementation of #[derive(PixLike)]
Documentation 
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#[macro_use]
extern crate quote;
extern crate proc_macro;
extern crate syn;

use proc_macro::TokenStream;
use std::iter;

#[proc_macro_derive(PixLike, attributes(size, total))]
pub fn pix_like(input: TokenStream) -> TokenStream {
    let s = input.to_string();
    let ast = syn::parse_macro_input(&s).unwrap();
    validate_input(&ast);
    let gen = impl_pix(&ast);
    gen.parse().unwrap()
}

fn validate_input(ast: &syn::MacroInput) {
    if let syn::Body::Struct(_) = ast.body {
        panic!("PixLike only works on Enums, not Structs.")
    }

    let _ = get_total_attr(&ast.attrs);
}

fn impl_pix(ast: &syn::MacroInput) -> quote::Tokens {
    let name = &ast.ident;
    let names = iter::repeat(name);
    let names_2 = iter::repeat(name);
    let variants = get_variants(ast);
    let variants_2 = get_variants(ast);
    let coords = get_coords(variants.len(), get_total_attr(&ast.attrs));

    quote! {
        impl PixLike for #name {
            fn pix_order() -> Vec<#name> {
                vec![
                    #(#names::#variants),*
                ]
            }

            fn get(&self) -> (f32, f32, f32, f32) {
                match *self {
                    #(#names_2::#variants_2 => #coords),*
                }
            }
        }

        impl std::default::Default for #name {
            fn default() -> #name {
                #name::Empty
            }
        }
    }
}

fn get_total_attr(attrs: &[syn::Attribute]) -> i32 {
    use syn::{Attribute, Ident, MetaItem};

    let eg = "e.g. `#[total = \"16\"]`";

    if let Some(attr) = attrs.iter().find(|attr| match attr.value {
        MetaItem::NameValue(ref ident, _) => *ident == Ident::from("total"),
        _ => false,
    }) {
        if let Attribute { value: MetaItem::NameValue(_, ref s), .. } = *attr {
            if let syn::Lit::Str(ref s, _) = *s {
                s.parse().unwrap_or_else(|_| {
                    panic!(
                        "Parsing to i32 failed on '{}'. Only stringed Integers are supported",
                        s
                    )
                })
            } else {
                panic!("Only String values are supported on Attributes {}", eg);
            }
        } else {
            panic!("Only NameValue Attributes are supported {}", eg);
        }
    } else {
        panic!("Must supply a total attribute {}", eg);
    }
}

fn get_variants(ast: &syn::MacroInput) -> Vec<syn::Ident> {
    match ast.body {
        syn::Body::Enum(ref variants) => variants.iter().cloned().map(|v| v.ident).collect(),
        _ => unreachable!(),
    }
}

fn get_coords(enum_count: usize, tileset_size: i32) -> Vec<(f32, f32, f32, f32)> {
    let tile_dim = (tileset_size as f32).sqrt() as i32;
    (0..enum_count)
        .map(|i| {
            let tex_coords = (i as i32 % tile_dim, i as i32 / tile_dim);
            get_tex_coords(tileset_size, tex_coords)
        })
        .collect::<Vec<_>>()
}

fn get_tex_coords(total_tiles: i32, loc: (i32, i32)) -> (f32, f32, f32, f32) {
    let tile_dim: f32 = (total_tiles as f32).sqrt();
    let per_tile: f32 = 1.0 / tile_dim;

    let top = 1.0 - loc.1 as f32 * per_tile;
    let right = (loc.0 + 1) as f32 * per_tile;
    let bottom = 1.0 - (loc.1 + 1) as f32 * per_tile;
    let left = loc.0 as f32 * per_tile;

    (top, right, bottom, left)
}