From 721ed95aa1c0622e4e6d9082bf25fd2024ee2aae Mon Sep 17 00:00:00 2001
From: Luca Versari <veluca93@gmail.com>
Date: Thu, 19 Sep 2024 03:07:44 +0200
Subject: [PATCH] Draft interface for a render pipeline.

---
 jxl/src/lib.rs        |   1 +
 jxl/src/render/mod.rs | 106 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 107 insertions(+)
 create mode 100644 jxl/src/render/mod.rs

diff --git a/jxl/src/lib.rs b/jxl/src/lib.rs
index bc36143..97f0a76 100644
--- a/jxl/src/lib.rs
+++ b/jxl/src/lib.rs
@@ -10,4 +10,5 @@ pub mod error;
 pub mod headers;
 pub mod icc;
 pub mod image;
+pub mod render;
 mod util;
diff --git a/jxl/src/render/mod.rs b/jxl/src/render/mod.rs
new file mode 100644
index 0000000..87d0273
--- /dev/null
+++ b/jxl/src/render/mod.rs
@@ -0,0 +1,106 @@
+use crate::{
+    error::Result,
+    image::{ImageDataType, ImageRectMut},
+};
+
+// All *_row_chunk functions here take one or two slices of slices.
+// The slices have as many entries as the number of used channels for the stage, i.e. the channels
+// for which `uses_channel` returns true.
+
+// These are the only stages that are assumed to have observable effects, i.e. calls to process_row
+// for other stages may be omitted if it can be shown they can't affect any Input stage process_row
+// call that happens inside image boundaries.
+pub trait RenderPipelineInputStage<InputT: ImageDataType> {
+    fn uses_channel(&self, c: usize) -> bool;
+    fn process_row_chunk(&mut self, position: (usize, usize), xsize: usize, row: &[&[InputT]]);
+}
+
+// Modifies channels in-place.
+pub trait RenderPipelineInPlaceStage<T: ImageDataType> {
+    fn uses_channel(&self, c: usize) -> bool;
+    fn process_row_chunk(&mut self, position: (usize, usize), xsize: usize, row: &mut [&mut [T]]);
+}
+
+// Modifies data and writes it to a new buffer, of possibly different type.
+pub trait RenderPipelineInOutStage<InputT: ImageDataType, OutputT: ImageDataType> {
+    // Amount of padding required on the input side.
+    const BORDER: (usize, usize);
+    // log2 of the number of rows/columns produced for each row/column of input.
+    const SHIFT: (usize, usize);
+
+    fn uses_channel(&self, c: usize) -> bool;
+
+    // For each channel:
+    //  - the input slice contains 1 + Self::BORDER.1 * 2 slices, each of length
+    //    xsize + Self::BORDER.0 * 2, i.e. covering one input row and up to BORDER pixels of
+    //    padding on either side.
+    //  - the output slice contains 1 << SHIFT.1 slices, each of length xsize << SHIFT.0, the
+    //    corresponding output pixels.
+    fn process_row_chunk(
+        &mut self,
+        position: (usize, usize),
+        xsize: usize,
+        input: &[&[&[InputT]]],
+        output: &mut [&mut [&mut [OutputT]]],
+    );
+}
+
+// Does not directly modify the current image pixels, but extends the current image with
+// additional data.
+pub trait RenderPipelineExtendStage<T: ImageDataType> {
+    // uses_channel is assumed to be always true
+    fn new_size(&self) -> (usize, usize);
+    fn original_data_origin(&self) -> (usize, usize);
+    // passed buffer must always be entirely outside of the original image.
+    fn fill_padding_row_chunk(
+        &mut self,
+        new_position: (usize, usize),
+        xsize: usize,
+        row: &mut [&mut [T]],
+    );
+}
+
+pub trait RenderPipelineBuilder: Sized {
+    type RenderPipeline: RenderPipeline;
+
+    fn new(num_channels: usize, size: (usize, usize), group_size: usize) -> Self;
+
+    fn add_input_stage<T: ImageDataType, Stage: RenderPipelineInputStage<T>>(
+        self,
+        stage: Stage,
+    ) -> Result<Self>;
+
+    fn add_inplace_stage<T: ImageDataType, Stage: RenderPipelineInPlaceStage<T>>(
+        self,
+        stage: Stage,
+    ) -> Result<Self>;
+
+    fn add_inout_stage<
+        InT: ImageDataType,
+        OutT: ImageDataType,
+        Stage: RenderPipelineInOutStage<InT, OutT>,
+    >(
+        self,
+        stage: Stage,
+    ) -> Result<Self>;
+
+    fn add_extend_stage<T: ImageDataType, Stage: RenderPipelineExtendStage<T>>(
+        self,
+        stage: Stage,
+    ) -> Result<Self>;
+
+    fn build(self) -> Self::RenderPipeline;
+}
+
+pub trait RenderPipeline {
+    type Builder: RenderPipelineBuilder<RenderPipeline = Self>;
+
+    // TODO(veluca): figure out a good multithreaded interface.
+    fn fill_group_input<T: ImageDataType, F: FnMut(ImageRectMut<T>, usize) -> bool>(
+        &mut self,
+        _group_id: usize,
+        _do_fill_group: F,
+    ) {
+        todo!()
+    }
+}