webgl.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

use euclid::{Rect, Size2D};
use gleam::gl;
use ipc_channel::ipc::{IpcBytesReceiver, IpcBytesSender};
use offscreen_gl_context::{GLContextAttributes, GLLimits};
use serde_bytes::ByteBuf;
use std::borrow::Cow;
use std::num::NonZeroU32;
use webrender_api::{DocumentId, ImageKey, PipelineId};

/// Helper function that creates a WebGL channel (WebGLSender, WebGLReceiver) to be used in WebGLCommands.
pub use crate::webgl_channel::webgl_channel;
/// Entry point channel type used for sending WebGLMsg messages to the WebGL renderer.
pub use crate::webgl_channel::WebGLChan;
/// Entry point type used in a Script Pipeline to get the WebGLChan to be used in that thread.
pub use crate::webgl_channel::WebGLPipeline;
/// Receiver type used in WebGLCommands.
pub use crate::webgl_channel::WebGLReceiver;
/// Result type for send()/recv() calls in in WebGLCommands.
pub use crate::webgl_channel::WebGLSendResult;
/// Sender type used in WebGLCommands.
pub use crate::webgl_channel::WebGLSender;

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct WebGLCommandBacktrace {
    #[cfg(feature = "webgl_backtrace")]
    pub backtrace: String,
    #[cfg(feature = "webgl_backtrace")]
    pub js_backtrace: Option<String>,
}

/// WebGL Message API
#[derive(Debug, Deserialize, Serialize)]
pub enum WebGLMsg {
    /// Creates a new WebGLContext.
    CreateContext(
        WebGLVersion,
        Size2D<u32>,
        GLContextAttributes,
        WebGLSender<Result<(WebGLCreateContextResult), String>>,
    ),
    /// Resizes a WebGLContext.
    ResizeContext(WebGLContextId, Size2D<u32>, WebGLSender<Result<(), String>>),
    /// Drops a WebGLContext.
    RemoveContext(WebGLContextId),
    /// Runs a WebGLCommand in a specific WebGLContext.
    WebGLCommand(WebGLContextId, WebGLCommand, WebGLCommandBacktrace),
    /// Runs a WebVRCommand in a specific WebGLContext.
    WebVRCommand(WebGLContextId, WebVRCommand),
    /// Locks a specific WebGLContext. Lock messages are used for a correct synchronization
    /// with WebRender external image API.
    /// WR locks a external texture when it wants to use the shared texture contents.
    /// The WR client should not change the shared texture content until the Unlock call.
    /// Currently OpenGL Sync Objects are used to implement the synchronization mechanism.
    Lock(WebGLContextId, WebGLSender<(u32, Size2D<i32>, usize)>),
    /// Unlocks a specific WebGLContext. Unlock messages are used for a correct synchronization
    /// with WebRender external image API.
    /// The WR unlocks a context when it finished reading the shared texture contents.
    /// Unlock messages are always sent after a Lock message.
    Unlock(WebGLContextId),
    /// Creates or updates the image keys required for WebRender.
    UpdateWebRenderImage(WebGLContextId, WebGLSender<ImageKey>),
    /// Commands used for the DOMToTexture feature.
    DOMToTextureCommand(DOMToTextureCommand),
    /// Frees all resources and closes the thread.
    Exit,
}

/// Contains the WebGLCommand sender and information about a WebGLContext
#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct WebGLCreateContextResult {
    /// Sender instance to send commands to the specific WebGLContext
    pub sender: WebGLMsgSender,
    /// Information about the internal GL Context.
    pub limits: GLLimits,
    /// How the WebGLContext is shared with WebRender.
    pub share_mode: WebGLContextShareMode,
    /// The GLSL version supported by the context.
    pub glsl_version: WebGLSLVersion,
}

#[derive(Clone, Copy, Debug, Deserialize, MallocSizeOf, Serialize)]
pub enum WebGLContextShareMode {
    /// Fast: a shared texture_id is used in WebRender.
    SharedTexture,
    /// Slow: glReadPixels is used to send pixels to WebRender each frame.
    Readback,
}

/// Defines the WebGL version
#[derive(Clone, Copy, Debug, Deserialize, Eq, MallocSizeOf, PartialEq, Serialize)]
pub enum WebGLVersion {
    /// https://www.khronos.org/registry/webgl/specs/1.0.2/
    /// Conforms closely to the OpenGL ES 2.0 API
    WebGL1,
    /// https://www.khronos.org/registry/webgl/specs/latest/2.0/
    /// Conforms closely to the OpenGL ES 3.0 API
    WebGL2,
}

/// Defines the GLSL version supported by the WebGL backend contexts.
#[derive(Clone, Copy, Debug, Deserialize, Eq, MallocSizeOf, PartialEq, Serialize)]
pub struct WebGLSLVersion {
    /// Major GLSL version
    pub major: u32,
    /// Minor GLSL version
    pub minor: u32,
}

/// Helper struct to send WebGLCommands to a specific WebGLContext.
#[derive(Clone, Debug, Deserialize, MallocSizeOf, Serialize)]
pub struct WebGLMsgSender {
    ctx_id: WebGLContextId,
    #[ignore_malloc_size_of = "channels are hard"]
    sender: WebGLChan,
}

impl WebGLMsgSender {
    pub fn new(id: WebGLContextId, sender: WebGLChan) -> Self {
        WebGLMsgSender {
            ctx_id: id,
            sender: sender,
        }
    }

    /// Returns the WebGLContextId associated to this sender
    pub fn context_id(&self) -> WebGLContextId {
        self.ctx_id
    }

    /// Send a WebGLCommand message
    #[inline]
    pub fn send(&self, command: WebGLCommand, backtrace: WebGLCommandBacktrace) -> WebGLSendResult {
        self.sender
            .send(WebGLMsg::WebGLCommand(self.ctx_id, command, backtrace))
    }

    /// Send a WebVRCommand message
    #[inline]
    pub fn send_vr(&self, command: WebVRCommand) -> WebGLSendResult {
        self.sender
            .send(WebGLMsg::WebVRCommand(self.ctx_id, command))
    }

    /// Send a resize message
    #[inline]
    pub fn send_resize(
        &self,
        size: Size2D<u32>,
        sender: WebGLSender<Result<(), String>>,
    ) -> WebGLSendResult {
        self.sender
            .send(WebGLMsg::ResizeContext(self.ctx_id, size, sender))
    }

    #[inline]
    pub fn send_remove(&self) -> WebGLSendResult {
        self.sender.send(WebGLMsg::RemoveContext(self.ctx_id))
    }

    #[inline]
    pub fn send_update_wr_image(&self, sender: WebGLSender<ImageKey>) -> WebGLSendResult {
        self.sender
            .send(WebGLMsg::UpdateWebRenderImage(self.ctx_id, sender))
    }

    pub fn send_dom_to_texture(&self, command: DOMToTextureCommand) -> WebGLSendResult {
        self.sender.send(WebGLMsg::DOMToTextureCommand(command))
    }
}

/// WebGL Commands for a specific WebGLContext
#[derive(Debug, Deserialize, Serialize)]
pub enum WebGLCommand {
    GetContextAttributes(WebGLSender<GLContextAttributes>),
    ActiveTexture(u32),
    BlendColor(f32, f32, f32, f32),
    BlendEquation(u32),
    BlendEquationSeparate(u32, u32),
    BlendFunc(u32, u32),
    BlendFuncSeparate(u32, u32, u32, u32),
    AttachShader(WebGLProgramId, WebGLShaderId),
    DetachShader(WebGLProgramId, WebGLShaderId),
    BindAttribLocation(WebGLProgramId, u32, String),
    BufferData(u32, IpcBytesReceiver, u32),
    BufferSubData(u32, isize, IpcBytesReceiver),
    Clear(u32),
    ClearColor(f32, f32, f32, f32),
    ClearDepth(f32),
    ClearStencil(i32),
    ColorMask(bool, bool, bool, bool),
    CullFace(u32),
    FrontFace(u32),
    DepthFunc(u32),
    DepthMask(bool),
    DepthRange(f32, f32),
    Enable(u32),
    Disable(u32),
    CompileShader(WebGLShaderId, String),
    CopyTexImage2D(u32, i32, u32, i32, i32, i32, i32, i32),
    CopyTexSubImage2D(u32, i32, i32, i32, i32, i32, i32, i32),
    CreateBuffer(WebGLSender<Option<WebGLBufferId>>),
    CreateFramebuffer(WebGLSender<Option<WebGLFramebufferId>>),
    CreateRenderbuffer(WebGLSender<Option<WebGLRenderbufferId>>),
    CreateTexture(WebGLSender<Option<WebGLTextureId>>),
    CreateProgram(WebGLSender<Option<WebGLProgramId>>),
    CreateShader(u32, WebGLSender<Option<WebGLShaderId>>),
    DeleteBuffer(WebGLBufferId),
    DeleteFramebuffer(WebGLFramebufferId),
    DeleteRenderbuffer(WebGLRenderbufferId),
    DeleteTexture(WebGLTextureId),
    DeleteProgram(WebGLProgramId),
    DeleteShader(WebGLShaderId),
    BindBuffer(u32, Option<WebGLBufferId>),
    BindFramebuffer(u32, WebGLFramebufferBindingRequest),
    BindRenderbuffer(u32, Option<WebGLRenderbufferId>),
    BindTexture(u32, Option<WebGLTextureId>),
    DisableVertexAttribArray(u32),
    EnableVertexAttribArray(u32),
    FramebufferRenderbuffer(u32, u32, u32, Option<WebGLRenderbufferId>),
    FramebufferTexture2D(u32, u32, u32, Option<WebGLTextureId>, i32),
    GetExtensions(WebGLSender<String>),
    GetShaderPrecisionFormat(u32, u32, WebGLSender<(i32, i32, i32)>),
    GetUniformLocation(WebGLProgramId, String, WebGLSender<i32>),
    GetShaderInfoLog(WebGLShaderId, WebGLSender<String>),
    GetProgramInfoLog(WebGLProgramId, WebGLSender<String>),
    GetFramebufferAttachmentParameter(u32, u32, u32, WebGLSender<i32>),
    GetRenderbufferParameter(u32, u32, WebGLSender<i32>),
    PolygonOffset(f32, f32),
    RenderbufferStorage(u32, u32, i32, i32),
    ReadPixels(Rect<u32>, u32, u32, IpcBytesSender),
    SampleCoverage(f32, bool),
    Scissor(i32, i32, u32, u32),
    StencilFunc(u32, i32, u32),
    StencilFuncSeparate(u32, u32, i32, u32),
    StencilMask(u32),
    StencilMaskSeparate(u32, u32),
    StencilOp(u32, u32, u32),
    StencilOpSeparate(u32, u32, u32, u32),
    Hint(u32, u32),
    LineWidth(f32),
    PixelStorei(u32, i32),
    LinkProgram(WebGLProgramId, WebGLSender<ProgramLinkInfo>),
    Uniform1f(i32, f32),
    Uniform1fv(i32, Vec<f32>),
    Uniform1i(i32, i32),
    Uniform1iv(i32, Vec<i32>),
    Uniform2f(i32, f32, f32),
    Uniform2fv(i32, Vec<f32>),
    Uniform2i(i32, i32, i32),
    Uniform2iv(i32, Vec<i32>),
    Uniform3f(i32, f32, f32, f32),
    Uniform3fv(i32, Vec<f32>),
    Uniform3i(i32, i32, i32, i32),
    Uniform3iv(i32, Vec<i32>),
    Uniform4f(i32, f32, f32, f32, f32),
    Uniform4fv(i32, Vec<f32>),
    Uniform4i(i32, i32, i32, i32, i32),
    Uniform4iv(i32, Vec<i32>),
    UniformMatrix2fv(i32, Vec<f32>),
    UniformMatrix3fv(i32, Vec<f32>),
    UniformMatrix4fv(i32, Vec<f32>),
    UseProgram(Option<WebGLProgramId>),
    ValidateProgram(WebGLProgramId),
    VertexAttrib(u32, f32, f32, f32, f32),
    VertexAttribPointer(u32, i32, u32, bool, i32, u32),
    VertexAttribPointer2f(u32, i32, bool, i32, u32),
    SetViewport(i32, i32, i32, i32),
    TexImage2D(u32, i32, i32, i32, i32, u32, u32, IpcBytesReceiver),
    TexSubImage2D(u32, i32, i32, i32, i32, i32, u32, u32, IpcBytesReceiver),
    DrawingBufferWidth(WebGLSender<i32>),
    DrawingBufferHeight(WebGLSender<i32>),
    Finish(WebGLSender<()>),
    Flush,
    GenerateMipmap(u32),
    CreateVertexArray(WebGLSender<Option<WebGLVertexArrayId>>),
    DeleteVertexArray(WebGLVertexArrayId),
    BindVertexArray(Option<WebGLVertexArrayId>),
    GetParameterBool(ParameterBool, WebGLSender<bool>),
    GetParameterBool4(ParameterBool4, WebGLSender<[bool; 4]>),
    GetParameterInt(ParameterInt, WebGLSender<i32>),
    GetParameterInt2(ParameterInt2, WebGLSender<[i32; 2]>),
    GetParameterInt4(ParameterInt4, WebGLSender<[i32; 4]>),
    GetParameterFloat(ParameterFloat, WebGLSender<f32>),
    GetParameterFloat2(ParameterFloat2, WebGLSender<[f32; 2]>),
    GetParameterFloat4(ParameterFloat4, WebGLSender<[f32; 4]>),
    GetProgramValidateStatus(WebGLProgramId, WebGLSender<bool>),
    GetProgramActiveUniforms(WebGLProgramId, WebGLSender<i32>),
    GetCurrentVertexAttrib(u32, WebGLSender<[f32; 4]>),
    GetTexParameterFloat(u32, TexParameterFloat, WebGLSender<f32>),
    GetTexParameterInt(u32, TexParameterInt, WebGLSender<i32>),
    TexParameteri(u32, u32, i32),
    TexParameterf(u32, u32, f32),
    DrawArrays {
        mode: u32,
        first: i32,
        count: i32,
    },
    DrawArraysInstanced {
        mode: u32,
        first: i32,
        count: i32,
        primcount: i32,
    },
    DrawElements {
        mode: u32,
        count: i32,
        type_: u32,
        offset: u32,
    },
    DrawElementsInstanced {
        mode: u32,
        count: i32,
        type_: u32,
        offset: u32,
        primcount: i32,
    },
    VertexAttribDivisor {
        index: u32,
        divisor: u32,
    },
    GetUniformBool(WebGLProgramId, i32, WebGLSender<bool>),
    GetUniformBool2(WebGLProgramId, i32, WebGLSender<[bool; 2]>),
    GetUniformBool3(WebGLProgramId, i32, WebGLSender<[bool; 3]>),
    GetUniformBool4(WebGLProgramId, i32, WebGLSender<[bool; 4]>),
    GetUniformInt(WebGLProgramId, i32, WebGLSender<i32>),
    GetUniformInt2(WebGLProgramId, i32, WebGLSender<[i32; 2]>),
    GetUniformInt3(WebGLProgramId, i32, WebGLSender<[i32; 3]>),
    GetUniformInt4(WebGLProgramId, i32, WebGLSender<[i32; 4]>),
    GetUniformFloat(WebGLProgramId, i32, WebGLSender<f32>),
    GetUniformFloat2(WebGLProgramId, i32, WebGLSender<[f32; 2]>),
    GetUniformFloat3(WebGLProgramId, i32, WebGLSender<[f32; 3]>),
    GetUniformFloat4(WebGLProgramId, i32, WebGLSender<[f32; 4]>),
    GetUniformFloat9(WebGLProgramId, i32, WebGLSender<[f32; 9]>),
    GetUniformFloat16(WebGLProgramId, i32, WebGLSender<[f32; 16]>),
    InitializeFramebuffer {
        color: bool,
        depth: bool,
        stencil: bool,
    },
}

macro_rules! define_resource_id_struct {
    ($name:ident) => {
        #[derive(Clone, Copy, Eq, Hash, PartialEq)]
        pub struct $name(NonZeroU32);

        impl $name {
            #[allow(unsafe_code)]
            #[inline]
            pub unsafe fn new(id: u32) -> Self {
                $name(NonZeroU32::new_unchecked(id))
            }

            #[inline]
            pub fn get(self) -> u32 {
                self.0.get()
            }
        }
    };
}

macro_rules! define_resource_id {
    ($name:ident) => {
        define_resource_id_struct!($name);

        #[allow(unsafe_code)]
        impl<'de> ::serde::Deserialize<'de> for $name {
            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
            where
                D: ::serde::Deserializer<'de>,
            {
                let id = u32::deserialize(deserializer)?;
                if id == 0 {
                    Err(::serde::de::Error::custom("expected a non-zero value"))
                } else {
                    Ok(unsafe { $name::new(id) })
                }
            }
        }

        impl ::serde::Serialize for $name {
            fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
            where
                S: ::serde::Serializer,
            {
                self.get().serialize(serializer)
            }
        }

        impl ::std::fmt::Debug for $name {
            fn fmt(&self, fmt: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
                fmt.debug_tuple(stringify!($name))
                    .field(&self.get())
                    .finish()
            }
        }

        impl ::std::fmt::Display for $name {
            fn fmt(&self, fmt: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
                write!(fmt, "{}", self.get())
            }
        }

        impl ::malloc_size_of::MallocSizeOf for $name {
            fn size_of(&self, _ops: &mut ::malloc_size_of::MallocSizeOfOps) -> usize {
                0
            }
        }
    };
}

define_resource_id!(WebGLBufferId);
define_resource_id!(WebGLFramebufferId);
define_resource_id!(WebGLRenderbufferId);
define_resource_id!(WebGLTextureId);
define_resource_id!(WebGLProgramId);
define_resource_id!(WebGLShaderId);
define_resource_id!(WebGLVertexArrayId);

#[derive(
    Clone, Copy, Debug, Deserialize, Eq, Hash, MallocSizeOf, Ord, PartialEq, PartialOrd, Serialize,
)]
pub struct WebGLContextId(pub usize);

#[derive(Clone, Copy, Debug, Deserialize, PartialEq, Serialize)]
pub enum WebGLError {
    InvalidEnum,
    InvalidFramebufferOperation,
    InvalidOperation,
    InvalidValue,
    OutOfMemory,
    ContextLost,
}

#[derive(Clone, Copy, Debug, Deserialize, Serialize)]
pub enum WebGLFramebufferBindingRequest {
    Explicit(WebGLFramebufferId),
    Default,
}

pub type WebGLResult<T> = Result<T, WebGLError>;

pub type WebVRDeviceId = u32;

// WebVR commands that must be called in the WebGL render thread.
#[derive(Clone, Debug, Deserialize, Serialize)]
pub enum WebVRCommand {
    /// Start presenting to a VR device.
    Create(WebVRDeviceId),
    /// Synchronize the pose information to be used in the frame.
    SyncPoses(WebVRDeviceId, f64, f64, WebGLSender<Result<ByteBuf, ()>>),
    /// Submit the frame to a VR device using the specified texture coordinates.
    SubmitFrame(WebVRDeviceId, [f32; 4], [f32; 4]),
    /// Stop presenting to a VR device
    Release(WebVRDeviceId),
}

// Trait object that handles WebVR commands.
// Receives the texture id and size associated to the WebGLContext.
pub trait WebVRRenderHandler: Send {
    fn handle(&mut self, command: WebVRCommand, texture: Option<(u32, Size2D<i32>)>);
}

/// WebGL commands required to implement DOMToTexture feature.
#[derive(Clone, Debug, Deserialize, Serialize)]
pub enum DOMToTextureCommand {
    /// Attaches a HTMLIFrameElement to a WebGLTexture.
    Attach(
        WebGLContextId,
        WebGLTextureId,
        DocumentId,
        PipelineId,
        Size2D<i32>,
    ),
    /// Releases the HTMLIFrameElement to WebGLTexture attachment.
    Detach(WebGLTextureId),
    /// Lock message used for a correct synchronization with WebRender GL flow.
    Lock(PipelineId, usize, WebGLSender<Option<(u32, Size2D<i32>)>>),
}

/// Information about a WebGL program linking operation.
#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct ProgramLinkInfo {
    /// Whether the program was linked successfully.
    pub linked: bool,
    /// The list of active attributes.
    pub active_attribs: Box<[ActiveAttribInfo]>,
    /// The list of active uniforms.
    pub active_uniforms: Box<[ActiveUniformInfo]>,
}

/// Description of a single active attribute.
#[derive(Clone, Debug, Deserialize, MallocSizeOf, Serialize)]
pub struct ActiveAttribInfo {
    /// The name of the attribute.
    pub name: String,
    /// The size of the attribute.
    pub size: i32,
    /// The type of the attribute.
    pub type_: u32,
    /// The location of the attribute.
    pub location: i32,
}

/// Description of a single active uniform.
#[derive(Clone, Debug, Deserialize, MallocSizeOf, Serialize)]
pub struct ActiveUniformInfo {
    /// The base name of the uniform.
    pub base_name: Box<str>,
    /// The size of the uniform, if it is an array.
    pub size: Option<i32>,
    /// The type of the uniform.
    pub type_: u32,
}

impl ActiveUniformInfo {
    pub fn name(&self) -> Cow<str> {
        if self.size.is_some() {
            let mut name = String::from(&*self.base_name);
            name.push_str("[0]");
            Cow::Owned(name)
        } else {
            Cow::Borrowed(&self.base_name)
        }
    }
}

macro_rules! parameters {
    ($name:ident { $(
        $variant:ident($kind:ident { $(
            $param:ident = gl::$value:ident,
        )+ }),
    )+ }) => {
        #[derive(Clone, Copy, Debug, Deserialize, Serialize)]
        pub enum $name { $(
            $variant($kind),
        )+}

        $(
            #[derive(Clone, Copy, Debug, Deserialize, Serialize)]
            #[repr(u32)]
            pub enum $kind { $(
                $param = gl::$value,
            )+}
        )+

        impl $name {
            pub fn from_u32(value: u32) -> WebGLResult<Self> {
                match value {
                    $($(gl::$value => Ok($name::$variant($kind::$param)),)+)+
                    _ => Err(WebGLError::InvalidEnum)
                }
            }
        }
    }
}

parameters! {
    Parameter {
        Bool(ParameterBool {
            DepthWritemask = gl::DEPTH_WRITEMASK,
            SampleCoverageInvert = gl::SAMPLE_COVERAGE_INVERT,
        }),
        Bool4(ParameterBool4 {
            ColorWritemask = gl::COLOR_WRITEMASK,
        }),
        Int(ParameterInt {
            ActiveTexture = gl::ACTIVE_TEXTURE,
            AlphaBits = gl::ALPHA_BITS,
            BlendDstAlpha = gl::BLEND_DST_ALPHA,
            BlendDstRgb = gl::BLEND_DST_RGB,
            BlendEquationAlpha = gl::BLEND_EQUATION_ALPHA,
            BlendEquationRgb = gl::BLEND_EQUATION_RGB,
            BlendSrcAlpha = gl::BLEND_SRC_ALPHA,
            BlendSrcRgb = gl::BLEND_SRC_RGB,
            BlueBits = gl::BLUE_BITS,
            CullFaceMode = gl::CULL_FACE_MODE,
            DepthBits = gl::DEPTH_BITS,
            DepthFunc = gl::DEPTH_FUNC,
            FragmentShaderDerivativeHint = gl::FRAGMENT_SHADER_DERIVATIVE_HINT,
            FrontFace = gl::FRONT_FACE,
            GenerateMipmapHint = gl::GENERATE_MIPMAP_HINT,
            GreenBits = gl::GREEN_BITS,
            RedBits = gl::RED_BITS,
            SampleBuffers = gl::SAMPLE_BUFFERS,
            Samples = gl::SAMPLES,
            StencilBackFail = gl::STENCIL_BACK_FAIL,
            StencilBackFunc = gl::STENCIL_BACK_FUNC,
            StencilBackPassDepthFail = gl::STENCIL_BACK_PASS_DEPTH_FAIL,
            StencilBackPassDepthPass = gl::STENCIL_BACK_PASS_DEPTH_PASS,
            StencilBackRef = gl::STENCIL_BACK_REF,
            StencilBackValueMask = gl::STENCIL_BACK_VALUE_MASK,
            StencilBackWritemask = gl::STENCIL_BACK_WRITEMASK,
            StencilBits = gl::STENCIL_BITS,
            StencilClearValue = gl::STENCIL_CLEAR_VALUE,
            StencilFail = gl::STENCIL_FAIL,
            StencilFunc = gl::STENCIL_FUNC,
            StencilPassDepthFail = gl::STENCIL_PASS_DEPTH_FAIL,
            StencilPassDepthPass = gl::STENCIL_PASS_DEPTH_PASS,
            StencilRef = gl::STENCIL_REF,
            StencilValueMask = gl::STENCIL_VALUE_MASK,
            StencilWritemask = gl::STENCIL_WRITEMASK,
            SubpixelBits = gl::SUBPIXEL_BITS,
        }),
        Int2(ParameterInt2 {
            MaxViewportDims = gl::MAX_VIEWPORT_DIMS,
        }),
        Int4(ParameterInt4 {
            ScissorBox = gl::SCISSOR_BOX,
            Viewport = gl::VIEWPORT,
        }),
        Float(ParameterFloat {
            DepthClearValue = gl::DEPTH_CLEAR_VALUE,
            LineWidth = gl::LINE_WIDTH,
            MaxTextureMaxAnisotropyExt = gl::MAX_TEXTURE_MAX_ANISOTROPY_EXT,
            PolygonOffsetFactor = gl::POLYGON_OFFSET_FACTOR,
            PolygonOffsetUnits = gl::POLYGON_OFFSET_UNITS,
            SampleCoverageValue = gl::SAMPLE_COVERAGE_VALUE,
        }),
        Float2(ParameterFloat2 {
            AliasedPointSizeRange = gl::ALIASED_POINT_SIZE_RANGE,
            AliasedLineWidthRange = gl::ALIASED_LINE_WIDTH_RANGE,
            DepthRange = gl::DEPTH_RANGE,
        }),
        Float4(ParameterFloat4 {
            BlendColor = gl::BLEND_COLOR,
            ColorClearValue = gl::COLOR_CLEAR_VALUE,
        }),
    }
}

parameters! {
    TexParameter {
        Float(TexParameterFloat {
            TextureMaxAnisotropyExt = gl::TEXTURE_MAX_ANISOTROPY_EXT,
        }),
        Int(TexParameterInt {
            TextureWrapS = gl::TEXTURE_WRAP_S,
            TextureWrapT = gl::TEXTURE_WRAP_T,
        }),
    }
}

pub fn is_gles() -> bool {
    // TODO: align this with the actual kind of graphics context in use, rather than
    // making assumptions based on platform
    cfg!(any(target_os = "android", target_os = "ios"))
}