eatgel/eatgel/src/shader.rs

use crate::err::Error;
use crate::GlContext;
use std::ffi::CString;
use std::ops::{Deref, DerefMut};
use std::os::raw::c_char;
use std::ptr::null;
use std::str::from_utf8;

pub trait ShaderData {
    fn init(&mut self, gl: &mut GlContext, program_id: u32);
    fn apply(&self, gl: &GlContext, program_id: u32);
}

impl ShaderData for () {
    fn init(&mut self, _gl: &mut GlContext, _program_id: u32) {}
    fn apply(&self, _gl: &GlContext, _program_id: u32) {}
}

pub struct ShaderProgram<D: ShaderData> {
    pub program_id: u32,
    data: D,
}

impl<D: ShaderData> ShaderProgram<D> {
    pub fn init(&mut self, gl: &mut GlContext) {
        self.data.init(gl, self.program_id);
    }

    pub fn apply(&self, gl: &GlContext) {
        self.data.apply(gl, self.program_id);
    }
}

impl<D: ShaderData> Deref for ShaderProgram<D> {
    type Target = D;

    fn deref(&self) -> &Self::Target {
        &self.data
    }
}

impl<D: ShaderData> DerefMut for ShaderProgram<D> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.data
    }
}

pub struct Shader(pub u32);

impl Drop for Shader {
    fn drop(&mut self) {
        unsafe { gl::DeleteShader(self.0) }
    }
}

#[repr(u32)]
pub enum ShaderType {
    Vertex = gl::VERTEX_SHADER,
    Fragment = gl::FRAGMENT_SHADER,
}

impl Shader {
    pub fn compile(shader_type: ShaderType, source: &str) -> Result<Shader, Error> {
        let shader_id = unsafe { gl::CreateShader(shader_type as u32) };
        let source = CString::new(source.as_bytes())?;
        unsafe {
            gl::ShaderSource(shader_id, 1, &source.as_ptr(), null());
            gl::CompileShader(shader_id);
            let mut success = 0;
            gl::GetShaderiv(shader_id, gl::COMPILE_STATUS, &mut success);

            if success != 1 {
                let mut log_length = 0;
                gl::GetShaderiv(shader_id, gl::INFO_LOG_LENGTH, &mut log_length);
                let mut log = Vec::with_capacity(log_length as usize);
                let mut len = 0;
                gl::GetShaderInfoLog(
                    shader_id,
                    log_length,
                    &mut len,
                    log.as_mut_ptr() as *mut c_char,
                );
                log.set_len(len as usize);

                return Err(Error::ShaderCompilationFailure(
                    from_utf8(&log)?.to_string(),
                ));
            }
        }

        Ok(Shader(shader_id))
    }
}

impl ShaderProgram<()> {
    pub fn create(shader0: Shader, shader1: Shader) -> Result<ShaderProgram<()>, Error> {
        ShaderProgram::create_with_data((), shader0, shader1)
    }
}

impl<D: ShaderData> ShaderProgram<D> {
    pub fn enable(&self) {
        unsafe { gl::UseProgram(self.program_id) }
    }

    pub fn create_with_data(
        data: D,
        shader0: Shader,
        shader1: Shader,
    ) -> Result<ShaderProgram<D>, Error> {
        unsafe {
            let program_id = gl::CreateProgram();
            gl::AttachShader(program_id, shader0.0);
            gl::AttachShader(program_id, shader1.0);
            gl::LinkProgram(program_id);

            let mut status = 0;
            gl::GetProgramiv(program_id, gl::LINK_STATUS, &mut status);
            if status != 1 {
                let mut log_length = 0;
                gl::GetProgramiv(program_id, gl::INFO_LOG_LENGTH, &mut log_length);
                let mut log = Vec::with_capacity(log_length as usize);
                let mut len = 0;
                gl::GetProgramInfoLog(
                    program_id,
                    log_length,
                    &mut len,
                    log.as_mut_ptr() as *mut c_char,
                );

                log.set_len(len as usize);

                return Err(Error::ShaderProgramLinkFailure(
                    from_utf8(&log)?.to_string(),
                ));
            }

            gl::DeleteShader(shader0.0);
            gl::DeleteShader(shader1.0);

            Ok(ShaderProgram { data, program_id })
        }
    }
}