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glium 0.34.0

Elegant and safe OpenGL wrapper. Glium is an intermediate layer between OpenGL and your application. You still need to manually handle the graphics pipeline, but without having to use OpenGL's old and error-prone API. Its objectives: - Be safe to use. Many aspects of OpenGL that can trigger a crash if misused are automatically handled by glium. - Provide an API that enforces good pratices such as RAII or stateless function calls. - Be compatible with all OpenGL versions that support shaders, providing unified API when things diverge. - Avoid all OpenGL errors beforehand. - Produce optimized OpenGL function calls, and allow the user to easily use modern OpenGL techniques.
Documentation 
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use crate::fbo::{self, ValidatedAttachments};

use crate::context::Context;
use crate::ContextExt;
use crate::Rect;

use crate::QueryExt;
use crate::draw_parameters::TimeElapsedQuery;

use crate::Api;
use crate::version::Version;
use crate::gl;


pub fn clear(context: &Context, framebuffer: Option<&ValidatedAttachments<'_>>,
             rect: Option<&Rect>, color: Option<(f32, f32, f32, f32)>, color_srgb: bool,
             depth: Option<f32>, stencil: Option<i32>)
{
    unsafe {
        let mut ctxt = context.make_current();

        let fbo_id = fbo::FramebuffersContainer::get_framebuffer_for_drawing(&mut ctxt, framebuffer);
        fbo::bind_framebuffer(&mut ctxt, fbo_id, true, false);

        if ctxt.state.enabled_rasterizer_discard {
            ctxt.gl.Disable(gl::RASTERIZER_DISCARD);
            ctxt.state.enabled_rasterizer_discard = false;
        }

        if ctxt.state.color_mask != (1, 1, 1, 1) {
            ctxt.state.color_mask = (1, 1, 1, 1);
            ctxt.gl.ColorMask(1, 1, 1, 1);
        }

        if ctxt.version >= &Version(Api::Gl, 3, 0) || ctxt.extensions.gl_arb_framebuffer_srgb ||
           ctxt.extensions.gl_ext_framebuffer_srgb || ctxt.extensions.gl_ext_srgb_write_control
        {
            if !color_srgb && !ctxt.state.enabled_framebuffer_srgb {
                ctxt.gl.Enable(gl::FRAMEBUFFER_SRGB);
                ctxt.state.enabled_framebuffer_srgb = true;

            } else if color_srgb && ctxt.state.enabled_framebuffer_srgb {
                ctxt.gl.Disable(gl::FRAMEBUFFER_SRGB);
                ctxt.state.enabled_framebuffer_srgb = false;
            }
        }

        TimeElapsedQuery::end_conditional_render(&mut ctxt);

        if let Some(rect) = rect {
            let rect = (rect.left as gl::types::GLint, rect.bottom as gl::types::GLint,
                        rect.width as gl::types::GLsizei, rect.height as gl::types::GLsizei);

            if ctxt.state.scissor != Some(rect) {
                ctxt.gl.Scissor(rect.0, rect.1, rect.2, rect.3);
                ctxt.state.scissor = Some(rect);
            }

            if !ctxt.state.enabled_scissor_test {
                ctxt.gl.Enable(gl::SCISSOR_TEST);
                ctxt.state.enabled_scissor_test = true;
            }

        } else if ctxt.state.enabled_scissor_test {
            ctxt.gl.Disable(gl::SCISSOR_TEST);
            ctxt.state.enabled_scissor_test = false;
        }

        let mut flags = 0;

        if let Some(color) = color {
            let color = (color.0 as gl::types::GLclampf, color.1 as gl::types::GLclampf,
                         color.2 as gl::types::GLclampf, color.3 as gl::types::GLclampf);

            flags |= gl::COLOR_BUFFER_BIT;

            if ctxt.state.clear_color != color {
                ctxt.gl.ClearColor(color.0, color.1, color.2, color.3);
                ctxt.state.clear_color = color;
            }
        }

        if let Some(depth) = depth {
            let depth = depth as gl::types::GLclampf;

            flags |= gl::DEPTH_BUFFER_BIT;

            if ctxt.state.clear_depth != depth {
                if ctxt.version >= &Version(Api::Gl, 1, 0) {
                    ctxt.gl.ClearDepth(depth as gl::types::GLclampd);
                } else if ctxt.version >= &Version(Api::GlEs, 2, 0) {
                    ctxt.gl.ClearDepthf(depth);
                } else {
                    unreachable!();
                }

                ctxt.state.clear_depth = depth;
            }

            if !ctxt.state.depth_mask {
                ctxt.gl.DepthMask(gl::TRUE);
                ctxt.state.depth_mask = true;
            }
        }

        if let Some(stencil) = stencil {
            let stencil = stencil as gl::types::GLint;

            flags |= gl::STENCIL_BUFFER_BIT;

            if ctxt.state.clear_stencil != stencil {
                ctxt.gl.ClearStencil(stencil);
                ctxt.state.clear_stencil = stencil;
            }
        }

        ctxt.gl.Clear(flags);
    }
}