webgl: Refactor texture validations to take advantage of rust type system

This commit introduces the `WebGLValidator` trait, and uses it for multiple
validations in the texture-related WebGL code, to move that logic out of the
already bloated `webglrenderingcontext.rs` file.

It also creates a type-safe wrapper for some WebGL types, removing all the
`unreachable!`s there, and introduces a macro for generating them conveniently.

This partially addresses #10693, pending refactor more code to use this
infrastructure, and (possibly?) introducing an `AsGLError` trait for the errors
to make the error handling happen in `WebGLContext`.

components/script/dom/webgl_validations/tex_image_2d.rs

@@ -0,0 +1,353 @@
+/* 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 dom::bindings::js::Root;
+use dom::webglrenderingcontext::WebGLRenderingContext;
+use dom::webgltexture::WebGLTexture;
+use std::{self, fmt};
+use super::WebGLValidator;
+use super::types::{TexImageTarget, TexDataType, TexFormat};
+use webrender_traits::WebGLError::*;
+
+/// The errors that the texImage* family of functions can generate.
+#[derive(Debug)]
+pub enum TexImageValidationError {
+    /// An invalid texture target was passed, it contains the invalid target.
+    InvalidTextureTarget(u32),
+    /// The passed texture target was not bound.
+    TextureTargetNotBound(u32),
+    /// Invalid texture dimensions were given.
+    InvalidCubicTextureDimensions,
+    /// A negative level was passed.
+    NegativeLevel,
+    /// A level too high to be allowed by the implementation was passed.
+    LevelTooHigh,
+    /// A negative width and height was passed.
+    NegativeDimension,
+    /// A bigger with and height were passed than what the implementation
+    /// allows.
+    TextureTooBig,
+    /// An invalid data type was passed.
+    InvalidDataType,
+    /// An invalid texture format was passed.
+    InvalidTextureFormat,
+    /// Format did not match internal_format.
+    TextureFormatMismatch,
+    /// Invalid data type for the given format.
+    InvalidTypeForFormat,
+    /// Invalid border
+    InvalidBorder,
+    /// Expected a power of two texture.
+    NonPotTexture,
+}
+
+impl std::error::Error for TexImageValidationError {
+    fn description(&self) -> &str {
+        use self::TexImageValidationError::*;
+        match *self {
+            InvalidTextureTarget(_)
+                => "Invalid texture target",
+            TextureTargetNotBound(_)
+                => "Texture was not bound",
+            InvalidCubicTextureDimensions
+                => "Invalid dimensions were given for a cubic texture target",
+            NegativeLevel
+                => "A negative level was passed",
+            LevelTooHigh
+                => "Level too high",
+            NegativeDimension
+                => "Negative dimensions were passed",
+            TextureTooBig
+                => "Dimensions given are too big",
+            InvalidDataType
+                => "Invalid data type",
+            InvalidTextureFormat
+                => "Invalid texture format",
+            TextureFormatMismatch
+                => "Texture format mismatch",
+            InvalidTypeForFormat
+                => "Invalid type for the given format",
+            InvalidBorder
+                => "Invalid border",
+            NonPotTexture
+                => "Expected a power of two texture",
+        }
+    }
+}
+
+impl fmt::Display for TexImageValidationError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "TexImageValidationError({})", std::error::Error::description(self))
+    }
+}
+
+fn log2(n: u32) -> u32 {
+    31 - n.leading_zeros()
+}
+
+pub struct CommonTexImage2DValidator<'a> {
+    context: &'a WebGLRenderingContext,
+    target: u32,
+    level: i32,
+    internal_format: u32,
+    width: i32,
+    height: i32,
+    border: i32,
+}
+
+pub struct CommonTexImage2DValidatorResult {
+    pub texture: Root<WebGLTexture>,
+    pub target: TexImageTarget,
+    pub level: u32,
+    pub internal_format: TexFormat,
+    pub width: u32,
+    pub height: u32,
+    pub border: u32,
+}
+
+impl<'a> WebGLValidator for CommonTexImage2DValidator<'a> {
+    type Error = TexImageValidationError;
+    type ValidatedOutput = CommonTexImage2DValidatorResult;
+    fn validate(self) -> Result<Self::ValidatedOutput, TexImageValidationError> {
+        // GL_INVALID_ENUM is generated if target is not GL_TEXTURE_2D,
+        // GL_TEXTURE_CUBE_MAP_POSITIVE_X, GL_TEXTURE_CUBE_MAP_NEGATIVE_X,
+        // GL_TEXTURE_CUBE_MAP_POSITIVE_Y, GL_TEXTURE_CUBE_MAP_NEGATIVE_Y,
+        // GL_TEXTURE_CUBE_MAP_POSITIVE_Z, or GL_TEXTURE_CUBE_MAP_NEGATIVE_Z.
+        let target = match TexImageTarget::from_gl_constant(self.target) {
+            Some(target) => target,
+            None => {
+                self.context.webgl_error(InvalidEnum);
+                return Err(TexImageValidationError::InvalidTextureTarget(self.target));
+            }
+        };
+
+        let texture = self.context.bound_texture_for_target(&target);
+        let limits = self.context.limits();
+
+        let max_size = if target.is_cubic() {
+             limits.max_cube_map_tex_size
+        } else {
+             limits.max_tex_size
+        };
+
+        //  If an attempt is made to call this function with no WebGLTexture
+        //  bound, an INVALID_OPERATION error is generated.
+        let texture = match texture {
+            Some(texture) => texture,
+            None => {
+                self.context.webgl_error(InvalidOperation);
+                return Err(TexImageValidationError::TextureTargetNotBound(self.target));
+            }
+        };
+
+        // GL_INVALID_ENUM is generated if internal_format is not an accepted
+        // format.
+        let internal_format = match TexFormat::from_gl_constant(self.internal_format) {
+            Some(format) => format,
+            None => {
+                self.context.webgl_error(InvalidEnum);
+                return Err(TexImageValidationError::InvalidTextureFormat);
+            }
+        };
+
+        // GL_INVALID_VALUE is generated if level is less than 0.
+        if self.level < 0 {
+            self.context.webgl_error(InvalidValue);
+            return Err(TexImageValidationError::NegativeLevel);
+        }
+
+        // GL_INVALID_VALUE is generated if width or height is less than 0
+        if self.width < 0 || self.height < 0 {
+            self.context.webgl_error(InvalidValue);
+            return Err(TexImageValidationError::NegativeDimension);
+        }
+
+        // GL_INVALID_VALUE is generated if width or height is greater than
+        // GL_MAX_TEXTURE_SIZE when target is GL_TEXTURE_2D or
+        // GL_MAX_CUBE_MAP_TEXTURE_SIZE when target is not GL_TEXTURE_2D.
+        if self.width as u32 > max_size || self.height as u32 > max_size {
+            self.context.webgl_error(InvalidValue);
+            return Err(TexImageValidationError::TextureTooBig);
+        }
+
+        let width = self.width as u32;
+        let height = self.height as u32;
+        let level = self.level as u32;
+
+        // GL_INVALID_VALUE is generated if level is greater than zero and the
+        // texture is not power of two.
+        if level > 0 && (!width.is_power_of_two() || !height.is_power_of_two()) {
+            self.context.webgl_error(InvalidValue);
+            return Err(TexImageValidationError::NonPotTexture);
+        }
+
+        // GL_INVALID_VALUE may be generated if level is greater than
+        // log_2(max), where max is the returned value of GL_MAX_TEXTURE_SIZE
+        // when target is GL_TEXTURE_2D or GL_MAX_CUBE_MAP_TEXTURE_SIZE when
+        // target is not GL_TEXTURE_2D.
+        if level > log2(max_size) {
+            self.context.webgl_error(InvalidValue);
+            return Err(TexImageValidationError::LevelTooHigh);
+        }
+
+        // GL_INVALID_VALUE is generated if border is not 0.
+        if self.border != 0 {
+            self.context.webgl_error(InvalidValue);
+            return Err(TexImageValidationError::InvalidBorder);
+        }
+
+        Ok(CommonTexImage2DValidatorResult {
+            texture: texture,
+            target: target,
+            level: level,
+            internal_format: internal_format,
+            width: width,
+            height: height,
+            border: self.border as u32,
+        })
+    }
+}
+
+impl<'a> CommonTexImage2DValidator<'a> {
+    pub fn new(context: &'a WebGLRenderingContext,
+               target: u32, level: i32,
+               internal_format: u32,
+               width: i32, height: i32,
+               border: i32) -> Self {
+        CommonTexImage2DValidator {
+            context: context,
+            target: target,
+            level: level,
+            internal_format: internal_format,
+            width: width,
+            height: height,
+            border: border
+        }
+    }
+}
+
+pub struct TexImage2DValidator<'a> {
+    common_validator: CommonTexImage2DValidator<'a>,
+    format: u32,
+    data_type: u32,
+}
+
+impl<'a> TexImage2DValidator<'a> {
+    // TODO: Move data validation logic here.
+    pub fn new(context: &'a WebGLRenderingContext,
+               target: u32,
+               level: i32,
+               internal_format: u32,
+               width: i32,
+               height: i32,
+               border: i32,
+               format: u32,
+               data_type: u32) -> Self {
+        TexImage2DValidator {
+            common_validator: CommonTexImage2DValidator::new(context, target,
+                                                             level,
+                                                             internal_format,
+                                                             width, height,
+                                                             border),
+            format: format,
+            data_type: data_type,
+        }
+    }
+}
+
+/// The validated result of a TexImage2DValidator-validated call.
+pub struct TexImage2DValidatorResult {
+    /// NB: width, height and level are already unsigned after validation.
+    pub width: u32,
+    pub height: u32,
+    pub level: u32,
+    pub border: u32,
+    pub texture: Root<WebGLTexture>,
+    pub target: TexImageTarget,
+    pub format: TexFormat,
+    pub data_type: TexDataType,
+}
+
+/// TexImage2d validator as per
+/// https://www.khronos.org/opengles/sdk/docs/man/xhtml/glTexImage2D.xml
+impl<'a> WebGLValidator for TexImage2DValidator<'a> {
+    type ValidatedOutput = TexImage2DValidatorResult;
+    type Error = TexImageValidationError;
+
+    fn validate(self) -> Result<Self::ValidatedOutput, TexImageValidationError> {
+        let context = self.common_validator.context;
+        let CommonTexImage2DValidatorResult {
+            texture,
+            target,
+            level,
+            internal_format,
+            width,
+            height,
+            border,
+        } = try!(self.common_validator.validate());
+
+        // GL_INVALID_VALUE is generated if target is one of the six cube map 2D
+        // image targets and the width and height parameters are not equal.
+        if target.is_cubic() && width != height {
+            context.webgl_error(InvalidValue);
+            return Err(TexImageValidationError::InvalidCubicTextureDimensions);
+        }
+
+        // GL_INVALID_ENUM is generated if format or data_type is not an
+        // accepted value.
+        let data_type = match TexDataType::from_gl_constant(self.data_type) {
+            Some(data_type) => data_type,
+            None => {
+                context.webgl_error(InvalidEnum);
+                return Err(TexImageValidationError::InvalidDataType);
+            },
+        };
+
+        let format = match TexFormat::from_gl_constant(self.format) {
+            Some(format) => format,
+            None => {
+                context.webgl_error(InvalidEnum);
+                return Err(TexImageValidationError::InvalidTextureFormat);
+            }
+        };
+
+        // GL_INVALID_OPERATION is generated if format does not match
+        // internal_format.
+        if format != internal_format {
+            context.webgl_error(InvalidOperation);
+            return Err(TexImageValidationError::TextureFormatMismatch);
+        }
+
+
+        // GL_INVALID_OPERATION is generated if type is
+        // GL_UNSIGNED_SHORT_4_4_4_4 or GL_UNSIGNED_SHORT_5_5_5_1 and format is
+        // not GL_RGBA.
+        //
+        // GL_INVALID_OPERATION is generated if type is GL_UNSIGNED_SHORT_5_6_5
+        // and format is not GL_RGB.
+        match data_type {
+            TexDataType::UnsignedShort4444 |
+            TexDataType::UnsignedShort5551 if format != TexFormat::RGBA => {
+                context.webgl_error(InvalidOperation);
+                return Err(TexImageValidationError::InvalidTypeForFormat);
+            },
+            TexDataType::UnsignedShort565 if format != TexFormat::RGB => {
+                context.webgl_error(InvalidOperation);
+                return Err(TexImageValidationError::InvalidTypeForFormat);
+            },
+            _ => {},
+        }
+
+        Ok(TexImage2DValidatorResult {
+            width: width,
+            height: height,
+            level: level,
+            border: border,
+            texture: texture,
+            target: target,
+            format: format,
+            data_type: data_type,
+        })
+    }
+}