appy 0.1.6

Declarative UI framework with native rendering
Documentation 
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use crate::gl;
use crate::gl::types::*;
use std::ffi::CString;

fn compile_shader(source: String, kind: GLuint) -> GLuint {
    let str_source = CString::new(&*source).unwrap();
    let shader_id = unsafe { gl::CreateShader(kind) };

    unsafe {
        gl::ShaderSource(shader_id, 1, &str_source.as_ptr(), std::ptr::null());
        gl::CompileShader(shader_id);
    }

    let mut success: gl::types::GLint = 1;
    unsafe {
        gl::GetShaderiv(shader_id, gl::COMPILE_STATUS, &mut success);
    }

    if success == 0 {
        let mut len: gl::types::GLint = 0;
        unsafe {
            gl::GetShaderiv(shader_id, gl::INFO_LOG_LENGTH, &mut len);
        }
        //log_debug!("l={}",len);

        let mut buffer: Vec<u8> = Vec::with_capacity(len as usize + 10);
        buffer.extend([b' '].iter().cycle().take(len as usize));
        let error: CString = unsafe { CString::from_vec_unchecked(buffer) };

        let mut len_out: gl::types::GLint = 0;

        unsafe {
            gl::GetShaderInfoLog(
                shader_id,
                len + 5,
                &mut len_out,
                error.as_ptr() as *mut gl::types::GLchar,
            );
        }

        let s = error.to_string_lossy();
        panic!("Unable to compile shader: {:?}", s);
    }

    shader_id
}

/// Abstraction for an OpenGL shader program.
pub struct ShaderProgram {
    program_id: GLuint,
}

/// The source of a vertex or fragment shader.
pub enum ShaderSource {
    VertexShader(String),
    FragmentShader(String),
}

impl ShaderProgram {
    /// Create a shader program containing a number of
    /// shader sources.
    pub fn new(sources: Vec<ShaderSource>) -> Self {
        let program_id = unsafe { gl::CreateProgram() };

        for source in sources {
            let shader_id = match source {
                ShaderSource::VertexShader(source_text) => {
                    compile_shader(source_text, gl::VERTEX_SHADER)
                }

                ShaderSource::FragmentShader(source_text) => {
                    compile_shader(source_text, gl::FRAGMENT_SHADER)
                }
            };

            unsafe { gl::AttachShader(program_id, shader_id) };
        }

        unsafe { gl::LinkProgram(program_id) };

        Self { program_id }
    }

    /// Use this program.
    pub fn use_program(&self) {
        unsafe {
            gl::UseProgram(self.program_id);
        }
    }

    /// The the location of a uniform.
    pub fn get_uniform_location(&self, name: &str) -> i32 {
        //self.ensure_linked();

        let s = CString::new(name).unwrap();
        let loc: i32;

        unsafe {
            loc = gl::GetUniformLocation(self.program_id, s.as_ptr());
        }

        if loc < 0 {
            panic!("Can't find uniform: {}", name)
        }

        loc
    }

    /// The the location of an attrib.
    pub fn get_attrib_location(&self, name: &str) -> i32 {
        //self.ensure_linked();

        let s = CString::new(name).unwrap();
        let loc: i32;

        unsafe {
            loc = gl::GetAttribLocation(self.program_id, s.as_ptr());
        }

        if loc < 0 {
            panic!("Can't find attrib: {}", name)
        }

        loc
    }
}