Auto merge of #24783 - mmatyas:webgl_fns_readpixels, r=nox

Add support for WebGL2 ReadPixels functions

Adds support for the new ReadPixels functions introduced with WebGL2 and the relevant PixelStorei parameters..

Reference: https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.10

<!-- Please describe your changes on the following line: -->

---

This is a work in progress patch, but I think it might be ready for comments. There are a few issues left:

- When the target is the pixel pack buffer, the GL function expects a byte offset as a pointer. In Sparkle the `read_pixels` functions return/work on top of arrays, so for now I've made a [workaround patch](45d8bb263d). I wonder if that's okay or should we do it somehow differently?
- When writing to the pixel pack buffer, padding bytes on the destination are properly ignored. When writing to client buffers, Sparkle `read_pixels` returns a buffer with 1 byte alignment, which I think is fine (less stuff to move between threads), but requires positioning the rows manually (see the bottom of `read_pixels_into` vs. `ReadPixels_`).
- There are some duplicated code between the array buffer and pixel pack buffer variants, eg. the detection of intersection with the framebuffer. This could be refactored, but that results in a function with `Result<Option<Rect<u32>>, WebGLError>`, which I'm not sure is readable enough to help.
- There is a duplication with the WebGL1 code. WebGL2 introduces row length, skip pixels and skip rows as pixel pack parameters which affect the ReadPixels operation. The helper functions could be moved to be usable in WebGL1, but then these new modifiers would also need to be passed as a function parameter, which is somewhat ugly (but would work). What's your opinion about this?

cc @jdm @zakorgy

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] There are tests for these changes

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components/script/dom/webgl2renderingcontext.rs

@@ -25,7 +25,7 @@ use crate::dom::webglprogram::WebGLProgram;
 use crate::dom::webglquery::WebGLQuery;
 use crate::dom::webglrenderbuffer::WebGLRenderbuffer;
 use crate::dom::webglrenderingcontext::{
-    LayoutCanvasWebGLRenderingContextHelpers, WebGLRenderingContext,
+    LayoutCanvasWebGLRenderingContextHelpers, Size2DExt, WebGLRenderingContext,
 };
 use crate::dom::webglsampler::{WebGLSampler, WebGLSamplerValue};
 use crate::dom::webglshader::WebGLShader;
@@ -42,13 +42,15 @@ use canvas_traits::webgl::{
     webgl_channel, GLContextAttributes, WebGLCommand, WebGLResult, WebGLVersion,
 };
 use dom_struct::dom_struct;
-use euclid::default::Size2D;
+use euclid::default::{Point2D, Rect, Size2D};
 use ipc_channel::ipc;
 use js::jsapi::{JSObject, Type};
 use js::jsval::{BooleanValue, DoubleValue, Int32Value, JSVal, NullValue, UInt32Value};
 use js::rust::CustomAutoRooterGuard;
 use js::typedarray::ArrayBufferView;
 use script_layout_interface::HTMLCanvasDataSource;
+use std::cell::Cell;
+use std::cmp;
 use std::ptr::NonNull;
 
 #[dom_struct]
@@ -65,6 +67,9 @@ pub struct WebGL2RenderingContext {
     bound_transform_feedback_buffer: MutNullableDom<WebGLBuffer>,
     bound_uniform_buffer: MutNullableDom<WebGLBuffer>,
     current_transform_feedback: MutNullableDom<WebGLTransformFeedback>,
+    texture_pack_row_length: Cell<usize>,
+    texture_pack_skip_pixels: Cell<usize>,
+    texture_pack_skip_rows: Cell<usize>,
 }
 
 fn typedarray_elem_size(typeid: Type) -> usize {
@@ -77,6 +82,17 @@ fn typedarray_elem_size(typeid: Type) -> usize {
     }
 }
 
+struct ReadPixelsAllowedFormats<'a> {
+    array_types: &'a [Type],
+    channels: usize,
+}
+
+struct ReadPixelsSizes {
+    row_stride: usize,
+    skipped_bytes: usize,
+    size: usize,
+}
+
 impl WebGL2RenderingContext {
     fn new_inherited(
         window: &Window,
@@ -104,6 +120,9 @@ impl WebGL2RenderingContext {
             bound_transform_feedback_buffer: MutNullableDom::new(None),
             bound_uniform_buffer: MutNullableDom::new(None),
             current_transform_feedback: MutNullableDom::new(None),
+            texture_pack_row_length: Cell::new(0),
+            texture_pack_skip_pixels: Cell::new(0),
+            texture_pack_skip_rows: Cell::new(0),
         })
     }
 
@@ -147,6 +166,213 @@ impl WebGL2RenderingContext {
             slot.set(None);
         }
     }
+
+    fn calc_read_pixel_formats(
+        &self,
+        pixel_type: u32,
+        format: u32,
+    ) -> WebGLResult<ReadPixelsAllowedFormats> {
+        let array_types = match pixel_type {
+            constants::BYTE => &[Type::Int8][..],
+            constants::SHORT => &[Type::Int16][..],
+            constants::INT => &[Type::Int32][..],
+            constants::UNSIGNED_BYTE => &[Type::Uint8, Type::Uint8Clamped][..],
+            constants::UNSIGNED_SHORT |
+            constants::UNSIGNED_SHORT_4_4_4_4 |
+            constants::UNSIGNED_SHORT_5_5_5_1 |
+            constants::UNSIGNED_SHORT_5_6_5 => &[Type::Uint16][..],
+            constants::UNSIGNED_INT |
+            constants::UNSIGNED_INT_2_10_10_10_REV |
+            constants::UNSIGNED_INT_10F_11F_11F_REV |
+            constants::UNSIGNED_INT_5_9_9_9_REV => &[Type::Uint32][..],
+            constants::FLOAT => &[Type::Float32][..],
+            constants::HALF_FLOAT => &[Type::Uint16][..],
+            _ => return Err(InvalidEnum),
+        };
+        let channels = match format {
+            constants::ALPHA | constants::RED | constants::RED_INTEGER => 1,
+            constants::RG | constants::RG_INTEGER => 2,
+            constants::RGB | constants::RGB_INTEGER => 3,
+            constants::RGBA | constants::RGBA_INTEGER => 4,
+            _ => return Err(InvalidEnum),
+        };
+        Ok(ReadPixelsAllowedFormats {
+            array_types,
+            channels,
+        })
+    }
+
+    fn calc_read_pixel_sizes(
+        &self,
+        width: i32,
+        height: i32,
+        bytes_per_pixel: usize,
+    ) -> WebGLResult<ReadPixelsSizes> {
+        if width < 0 || height < 0 {
+            return Err(InvalidValue);
+        }
+
+        // See also https://www.khronos.org/registry/webgl/specs/latest/2.0/#5.36
+        let pixels_per_row = if self.texture_pack_row_length.get() > 0 {
+            self.texture_pack_row_length.get()
+        } else {
+            width as usize
+        };
+        if self.texture_pack_skip_pixels.get() + width as usize > pixels_per_row {
+            return Err(InvalidOperation);
+        }
+
+        let bytes_per_row = pixels_per_row
+            .checked_mul(bytes_per_pixel)
+            .ok_or(InvalidOperation)?;
+        let row_padding_bytes = {
+            let pack_alignment = self.base.get_texture_packing_alignment() as usize;
+            match bytes_per_row % pack_alignment {
+                0 => 0,
+                remainder => pack_alignment - remainder,
+            }
+        };
+        let row_stride = bytes_per_row + row_padding_bytes;
+        let size = if width == 0 || height == 0 {
+            0
+        } else {
+            let full_row_bytes = row_stride
+                .checked_mul(height as usize - 1)
+                .ok_or(InvalidOperation)?;
+            let last_row_bytes = bytes_per_pixel
+                .checked_mul(width as usize)
+                .ok_or(InvalidOperation)?;
+            let result = full_row_bytes
+                .checked_add(last_row_bytes)
+                .ok_or(InvalidOperation)?;
+            result
+        };
+        let skipped_bytes = {
+            let skipped_row_bytes = self
+                .texture_pack_skip_rows
+                .get()
+                .checked_mul(row_stride)
+                .ok_or(InvalidOperation)?;
+            let skipped_pixel_bytes = self
+                .texture_pack_skip_pixels
+                .get()
+                .checked_mul(bytes_per_pixel)
+                .ok_or(InvalidOperation)?;
+            let result = skipped_row_bytes
+                .checked_add(skipped_pixel_bytes)
+                .ok_or(InvalidOperation)?;
+            result
+        };
+        Ok(ReadPixelsSizes {
+            row_stride,
+            skipped_bytes,
+            size,
+        })
+    }
+
+    #[allow(unsafe_code)]
+    fn read_pixels_into(
+        &self,
+        x: i32,
+        y: i32,
+        width: i32,
+        height: i32,
+        format: u32,
+        pixel_type: u32,
+        dst: &mut ArrayBufferView,
+        dst_elem_offset: u32,
+    ) {
+        handle_potential_webgl_error!(self.base, self.base.validate_framebuffer(), return);
+
+        if self.bound_pixel_pack_buffer.get().is_some() {
+            return self.base.webgl_error(InvalidOperation);
+        }
+
+        let dst_byte_offset = {
+            let dst_elem_size = typedarray_elem_size(dst.get_array_type());
+            dst_elem_offset as usize * dst_elem_size
+        };
+        if dst_byte_offset > dst.len() {
+            return self.base.webgl_error(InvalidValue);
+        }
+
+        let dst_array_type = dst.get_array_type();
+        let ReadPixelsAllowedFormats {
+            array_types: allowed_array_types,
+            channels,
+        } = match self.calc_read_pixel_formats(pixel_type, format) {
+            Ok(result) => result,
+            Err(error) => return self.base.webgl_error(error),
+        };
+        if !allowed_array_types.contains(&dst_array_type) {
+            return self.base.webgl_error(InvalidOperation);
+        }
+        if format != constants::RGBA || pixel_type != constants::UNSIGNED_BYTE {
+            return self.base.webgl_error(InvalidOperation);
+        }
+
+        let bytes_per_pixel = typedarray_elem_size(dst_array_type) * channels;
+        let ReadPixelsSizes {
+            row_stride,
+            skipped_bytes,
+            size,
+        } = match self.calc_read_pixel_sizes(width, height, bytes_per_pixel) {
+            Ok(result) => result,
+            Err(error) => return self.base.webgl_error(error),
+        };
+        let dst_end = dst_byte_offset + skipped_bytes + size;
+        let dst_pixels = unsafe { dst.as_mut_slice() };
+        if dst_pixels.len() < dst_end {
+            return self.base.webgl_error(InvalidOperation);
+        }
+
+        let dst_byte_offset = {
+            let margin_left = cmp::max(0, -x) as usize;
+            let margin_top = cmp::max(0, -y) as usize;
+            dst_byte_offset +
+                skipped_bytes +
+                margin_left * bytes_per_pixel +
+                margin_top * row_stride
+        };
+        let src_rect = {
+            let (fb_width, fb_height) = handle_potential_webgl_error!(
+                self.base,
+                self.base
+                    .get_current_framebuffer_size()
+                    .ok_or(InvalidOperation),
+                return
+            );
+            let src_origin = Point2D::new(x, y);
+            let src_size = Size2D::new(width as u32, height as u32);
+            let fb_size = Size2D::new(fb_width as u32, fb_height as u32);
+            match pixels::clip(src_origin, src_size.to_u64(), fb_size.to_u64()) {
+                Some(rect) => rect.to_u32(),
+                None => return,
+            }
+        };
+        let src_row_bytes = handle_potential_webgl_error!(
+            self.base,
+            src_rect
+                .size
+                .width
+                .checked_mul(bytes_per_pixel as u32)
+                .ok_or(InvalidOperation),
+            return
+        );
+
+        let (sender, receiver) = ipc::bytes_channel().unwrap();
+        self.base.send_command(WebGLCommand::ReadPixels(
+            src_rect, format, pixel_type, sender,
+        ));
+        let src = receiver.recv().unwrap();
+
+        for i in 0..src_rect.size.height as usize {
+            let src_start = i * src_row_bytes as usize;
+            let dst_start = dst_byte_offset + i * row_stride;
+            dst_pixels[dst_start..dst_start + src_row_bytes as usize]
+                .copy_from_slice(&src[src_start..src_start + src_row_bytes as usize]);
+        }
+    }
 }
 
 impl WebGL2RenderingContextMethods for WebGL2RenderingContext {
@@ -936,9 +1162,18 @@ impl WebGL2RenderingContextMethods for WebGL2RenderingContext {
         self.base.LineWidth(width)
     }
 
-    /// https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.3
+    /// https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.2
     fn PixelStorei(&self, param_name: u32, param_value: i32) {
-        self.base.PixelStorei(param_name, param_value)
+        if param_value < 0 {
+            return self.base.webgl_error(InvalidValue);
+        }
+
+        match param_name {
+            constants::PACK_ROW_LENGTH => self.texture_pack_row_length.set(param_value as _),
+            constants::PACK_SKIP_PIXELS => self.texture_pack_skip_pixels.set(param_value as _),
+            constants::PACK_SKIP_ROWS => self.texture_pack_skip_rows.set(param_value as _),
+            _ => self.base.PixelStorei(param_name, param_value),
+        }
     }
 
     /// https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.3
@@ -955,10 +1190,128 @@ impl WebGL2RenderingContextMethods for WebGL2RenderingContext {
         height: i32,
         format: u32,
         pixel_type: u32,
-        pixels: CustomAutoRooterGuard<Option<ArrayBufferView>>,
+        mut pixels: CustomAutoRooterGuard<Option<ArrayBufferView>>,
     ) {
-        self.base
-            .ReadPixels(x, y, width, height, format, pixel_type, pixels)
+        let pixels =
+            handle_potential_webgl_error!(self.base, pixels.as_mut().ok_or(InvalidValue), return);
+
+        self.read_pixels_into(x, y, width, height, format, pixel_type, pixels, 0)
+    }
+
+    /// https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.10
+    fn ReadPixels_(
+        &self,
+        x: i32,
+        y: i32,
+        width: i32,
+        height: i32,
+        format: u32,
+        pixel_type: u32,
+        dst_byte_offset: i64,
+    ) {
+        handle_potential_webgl_error!(self.base, self.base.validate_framebuffer(), return);
+
+        let dst = match self.bound_pixel_pack_buffer.get() {
+            Some(buffer) => buffer,
+            None => return self.base.webgl_error(InvalidOperation),
+        };
+
+        if dst_byte_offset < 0 {
+            return self.base.webgl_error(InvalidValue);
+        }
+        let dst_byte_offset = dst_byte_offset as usize;
+        if dst_byte_offset > dst.capacity() {
+            return self.base.webgl_error(InvalidOperation);
+        }
+
+        let ReadPixelsAllowedFormats {
+            array_types: _,
+            channels: bytes_per_pixel,
+        } = match self.calc_read_pixel_formats(pixel_type, format) {
+            Ok(result) => result,
+            Err(error) => return self.base.webgl_error(error),
+        };
+        if format != constants::RGBA || pixel_type != constants::UNSIGNED_BYTE {
+            return self.base.webgl_error(InvalidOperation);
+        }
+
+        let ReadPixelsSizes {
+            row_stride: _,
+            skipped_bytes,
+            size,
+        } = match self.calc_read_pixel_sizes(width, height, bytes_per_pixel) {
+            Ok(result) => result,
+            Err(error) => return self.base.webgl_error(error),
+        };
+        let dst_end = dst_byte_offset + skipped_bytes + size;
+        if dst.capacity() < dst_end {
+            return self.base.webgl_error(InvalidOperation);
+        }
+
+        {
+            let (fb_width, fb_height) = handle_potential_webgl_error!(
+                self.base,
+                self.base
+                    .get_current_framebuffer_size()
+                    .ok_or(InvalidOperation),
+                return
+            );
+            let src_origin = Point2D::new(x, y);
+            let src_size = Size2D::new(width as u32, height as u32);
+            let fb_size = Size2D::new(fb_width as u32, fb_height as u32);
+            if pixels::clip(src_origin, src_size.to_u64(), fb_size.to_u64()).is_none() {
+                return;
+            }
+        }
+        let src_rect = Rect::new(Point2D::new(x, y), Size2D::new(width, height));
+
+        self.base.send_command(WebGLCommand::PixelStorei(
+            constants::PACK_ALIGNMENT,
+            self.base.get_texture_packing_alignment() as _,
+        ));
+        self.base.send_command(WebGLCommand::PixelStorei(
+            constants::PACK_ROW_LENGTH,
+            self.texture_pack_row_length.get() as _,
+        ));
+        self.base.send_command(WebGLCommand::PixelStorei(
+            constants::PACK_SKIP_ROWS,
+            self.texture_pack_skip_rows.get() as _,
+        ));
+        self.base.send_command(WebGLCommand::PixelStorei(
+            constants::PACK_SKIP_PIXELS,
+            self.texture_pack_skip_pixels.get() as _,
+        ));
+        self.base.send_command(WebGLCommand::ReadPixelsPP(
+            src_rect,
+            format,
+            pixel_type,
+            dst_byte_offset,
+        ));
+    }
+
+    /// https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.10
+    #[allow(unsafe_code)]
+    fn ReadPixels__(
+        &self,
+        x: i32,
+        y: i32,
+        width: i32,
+        height: i32,
+        format: u32,
+        pixel_type: u32,
+        mut dst: CustomAutoRooterGuard<ArrayBufferView>,
+        dst_elem_offset: u32,
+    ) {
+        self.read_pixels_into(
+            x,
+            y,
+            width,
+            height,
+            format,
+            pixel_type,
+            &mut dst,
+            dst_elem_offset,
+        )
     }
 
     /// https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.3

components/script/dom/webglrenderingcontext.rs

@@ -380,7 +380,7 @@ impl WebGLRenderingContext {
     //
     // The WebGL spec mentions a couple more operations that trigger
     // this: clear() and getParameter(IMPLEMENTATION_COLOR_READ_*).
-    fn validate_framebuffer(&self) -> WebGLResult<()> {
+    pub fn validate_framebuffer(&self) -> WebGLResult<()> {
         match self.bound_framebuffer.get() {
             Some(fb) => match fb.check_status_for_rendering() {
                 CompleteForRendering::Complete => Ok(()),
@@ -481,7 +481,7 @@ impl WebGLRenderingContext {
         self.send_command(WebGLCommand::VertexAttrib(indx, x, y, z, w));
     }
 
-    fn get_current_framebuffer_size(&self) -> Option<(i32, i32)> {
+    pub fn get_current_framebuffer_size(&self) -> Option<(i32, i32)> {
         match self.bound_framebuffer.get() {
             Some(fb) => return fb.size(),
 
@@ -490,6 +490,10 @@ impl WebGLRenderingContext {
         }
     }
 
+    pub fn get_texture_packing_alignment(&self) -> u8 {
+        self.texture_packing_alignment.get()
+    }
+
     // LINEAR filtering may be forbidden when using WebGL extensions.
     // https://www.khronos.org/registry/webgl/extensions/OES_texture_float_linear/
     fn validate_filterable_texture(

components/script/dom/webidls/WebGL2RenderingContext.webidl

@@ -497,10 +497,10 @@ interface mixin WebGL2RenderingContextBase
   void readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type,
                   /*[AllowShared]*/ ArrayBufferView? dstData);
   // WebGL2:
-  // void readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type,
-  //                 GLintptr offset);
-  // void readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type,
-  //                 [AllowShared] ArrayBufferView dstData, GLuint dstOffset);
+  void readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type,
+                  GLintptr offset);
+  void readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type,
+                  /*[AllowShared]*/ ArrayBufferView dstData, GLuint dstOffset);
 
   /* Multiple Render Targets */
   // void drawBuffers(sequence<GLenum> buffers);