egui_glow 0.20.1

#![allow(unsafe_code)]

use glow::HasContext as _;

use crate::check_for_gl_error;

// ----------------------------------------------------------------------------

#[derive(Debug)]
pub(crate) struct BufferInfo {
    pub location: u32, //
    pub vector_size: i32,
    pub data_type: u32, //GL_FLOAT,GL_UNSIGNED_BYTE
    pub normalized: bool,
    pub stride: i32,
    pub offset: i32,
}

// ----------------------------------------------------------------------------

/// Wrapper around either Emulated VAO or GL's VAO.
pub(crate) struct VertexArrayObject {
    // If `None`, we emulate VAO:s.
    vao: Option<crate::glow::VertexArray>,
    vbo: glow::Buffer,
    buffer_infos: Vec<BufferInfo>,
}

impl VertexArrayObject {
    #[allow(clippy::needless_pass_by_value)] // false positive
    pub(crate) unsafe fn new(
        gl: &glow::Context,
        vbo: glow::Buffer,
        buffer_infos: Vec<BufferInfo>,
    ) -> Self {
        let vao = if supports_vao(gl) {
            let vao = gl.create_vertex_array().unwrap();
            check_for_gl_error!(gl, "create_vertex_array");

            // Store state in the VAO:
            gl.bind_vertex_array(Some(vao));
            gl.bind_buffer(glow::ARRAY_BUFFER, Some(vbo));

            for attribute in &buffer_infos {
                gl.vertex_attrib_pointer_f32(
                    attribute.location,
                    attribute.vector_size,
                    attribute.data_type,
                    attribute.normalized,
                    attribute.stride,
                    attribute.offset,
                );
                check_for_gl_error!(gl, "vertex_attrib_pointer_f32");
                gl.enable_vertex_attrib_array(attribute.location);
                check_for_gl_error!(gl, "enable_vertex_attrib_array");
            }

            gl.bind_vertex_array(None);

            Some(vao)
        } else {
            tracing::debug!("VAO not supported");
            None
        };

        Self {
            vao,
            vbo,
            buffer_infos,
        }
    }

    pub(crate) unsafe fn bind(&self, gl: &glow::Context) {
        if let Some(vao) = self.vao {
            gl.bind_vertex_array(Some(vao));
            check_for_gl_error!(gl, "bind_vertex_array");
        } else {
            gl.bind_buffer(glow::ARRAY_BUFFER, Some(self.vbo));
            check_for_gl_error!(gl, "bind_buffer");

            for attribute in &self.buffer_infos {
                gl.vertex_attrib_pointer_f32(
                    attribute.location,
                    attribute.vector_size,
                    attribute.data_type,
                    attribute.normalized,
                    attribute.stride,
                    attribute.offset,
                );
                check_for_gl_error!(gl, "vertex_attrib_pointer_f32");
                gl.enable_vertex_attrib_array(attribute.location);
                check_for_gl_error!(gl, "enable_vertex_attrib_array");
            }
        }
    }

    pub(crate) unsafe fn unbind(&self, gl: &glow::Context) {
        if self.vao.is_some() {
            gl.bind_vertex_array(None);
        } else {
            gl.bind_buffer(glow::ARRAY_BUFFER, None);
            for attribute in &self.buffer_infos {
                gl.disable_vertex_attrib_array(attribute.location);
            }
        }
    }
}

// ----------------------------------------------------------------------------

fn supports_vao(gl: &glow::Context) -> bool {
    const WEBGL_PREFIX: &str = "WebGL ";
    const OPENGL_ES_PREFIX: &str = "OpenGL ES ";

    let version_string = unsafe { gl.get_parameter_string(glow::VERSION) };
    tracing::debug!("GL version: {:?}.", version_string);

    // Examples:
    // * "WebGL 2.0 (OpenGL ES 3.0 Chromium)"
    // * "WebGL 2.0"

    if let Some(pos) = version_string.rfind(WEBGL_PREFIX) {
        let version_str = &version_string[pos + WEBGL_PREFIX.len()..];
        if version_str.contains("1.0") {
            // need to test OES_vertex_array_object .
            let supported_extensions = gl.supported_extensions();
            tracing::debug!("Supported OpenGL extensions: {:?}", supported_extensions);
            supported_extensions.contains("OES_vertex_array_object")
                || supported_extensions.contains("GL_OES_vertex_array_object")
        } else {
            true
        }
    } else if version_string.contains(OPENGL_ES_PREFIX) {
        // glow targets es2.0+ so we don't concern about OpenGL ES-CM,OpenGL ES-CL
        if version_string.contains("2.0") {
            // need to test OES_vertex_array_object .
            let supported_extensions = gl.supported_extensions();
            tracing::debug!("Supported OpenGL extensions: {:?}", supported_extensions);
            supported_extensions.contains("OES_vertex_array_object")
                || supported_extensions.contains("GL_OES_vertex_array_object")
        } else {
            true
        }
    } else {
        // from OpenGL 3 vao into core
        if version_string.starts_with('2') {
            // I found APPLE_vertex_array_object , GL_ATI_vertex_array_object ,ARB_vertex_array_object
            // but APPLE's and ATI's very old extension.
            let supported_extensions = gl.supported_extensions();
            tracing::debug!("Supported OpenGL extensions: {:?}", supported_extensions);
            supported_extensions.contains("ARB_vertex_array_object")
                || supported_extensions.contains("GL_ARB_vertex_array_object")
        } else {
            true
        }
    }
}