Add several scaling modes for non-integer upscaling

examples/invaders/src/main.rs

@@ -122,13 +122,16 @@ fn main() -> Result<(), Error> {
         Arc::new(window)
     };
 
-    let pixels = {
+    let mut pixels = {
         let window_size = window.inner_size();
         let surface_texture =
             SurfaceTexture::new(window_size.width, window_size.height, Arc::clone(&window));
         Pixels::new(WIDTH as u32, HEIGHT as u32, surface_texture)?
     };
 
+    // Use the fill scaling mode which supports non-integer scaling.
+    pixels.set_scaling_mode(pixels::ScalingMode::Fill);
+
     let game = Game::new(pixels, debug);
 
     let res = game_loop(

shaders/scale.wgsl

@@ -7,6 +7,7 @@ struct VertexOutput {
 
 struct Locals {
     transform: mat4x4<f32>,
+    input_size: vec4<f32>
 }
 @group(0) @binding(2) var<uniform> r_locals: Locals;
 

shaders/scale_fill.wgsl

@@ -0,0 +1,40 @@
+// Vertex shader bindings
+
+struct VertexOutput {
+    @location(0) tex_coord: vec2<f32>,
+    @builtin(position) position: vec4<f32>,
+}
+
+struct Locals {
+    transform: mat4x4<f32>,
+    input_size: vec4<f32>
+}
+@group(0) @binding(2) var<uniform> r_locals: Locals;
+
+@vertex
+fn vs_main(
+    @location(0) position: vec2<f32>,
+) -> VertexOutput {
+    var out: VertexOutput;
+    // Output tex coord in texel coordinates (0..width, 0..height)
+    out.tex_coord = fma(position, vec2<f32>(0.5, -0.5), vec2<f32>(0.5, 0.5)) * r_locals.input_size.xy;
+    out.position = r_locals.transform * vec4<f32>(position, 0.0, 1.0);
+    return out;
+}
+
+// Fragment shader bindings
+
+@group(0) @binding(0) var r_tex_color: texture_2d<f32>;
+@group(0) @binding(1) var r_tex_sampler: sampler;
+
+@fragment
+fn fs_main(@location(0) tex_coord: vec2<f32>) -> @location(0) vec4<f32> {
+    let half = vec2<f32>(0.5);
+    let one = vec2<f32>(1.0);
+    let zero = vec2<f32>(0.0);
+    let texels_per_pixel = vec2<f32>(dpdx(tex_coord.x), dpdy(tex_coord.y));
+    let tex_coord_fract = fract(tex_coord);
+    let tex_coord_x = clamp(tex_coord_fract / texels_per_pixel, zero, half) + clamp((tex_coord_fract - one) / texels_per_pixel + half, zero, half);
+    let tex_coord_final = (floor(tex_coord) + tex_coord_x) * r_locals.input_size.zw;
+    return textureSample(r_tex_color, r_tex_sampler, tex_coord_final);
+}

src/builder.rs

@@ -1,5 +1,5 @@
 use crate::renderers::{ScalingMatrix, ScalingRenderer};
-use crate::{Error, Pixels, PixelsContext, SurfaceSize, SurfaceTexture, TextureError};
+use crate::{Error, Pixels, PixelsContext, ScalingMode, SurfaceSize, SurfaceTexture, TextureError};
 
 /// A builder to help create customized pixel buffers.
 pub struct PixelsBuilder<'req, 'dev, 'win, W: wgpu::WindowHandle + 'win> {
@@ -309,6 +309,7 @@ impl<'req, 'dev, 'win, W: wgpu::WindowHandle + 'win> PixelsBuilder<'req, 'dev, '
         let surface_size = self.surface_texture.size;
         let clear_color = self.clear_color;
         let blend_state = self.blend_state;
+        let scaling_mode = ScalingMode::PixelPerfect;
         let (scaling_matrix_inverse, texture_extent, texture, scaling_renderer, pixels_buffer_size) =
             create_backing_texture(
                 &device,
@@ -322,6 +323,7 @@ impl<'req, 'dev, 'win, W: wgpu::WindowHandle + 'win> PixelsBuilder<'req, 'dev, '
                 // Clear color and blending values
                 clear_color,
                 blend_state,
+                scaling_mode,
             )?;
 
         // Create the pixel buffer
@@ -432,6 +434,7 @@ pub(crate) fn create_backing_texture(
     render_texture_format: wgpu::TextureFormat,
     clear_color: wgpu::Color,
     blend_state: wgpu::BlendState,
+    scaling_mode: ScalingMode,
 ) -> Result<
     (
         ultraviolet::Mat4,
@@ -447,6 +450,7 @@ pub(crate) fn create_backing_texture(
     let scaling_matrix_inverse = ScalingMatrix::new(
         (width as f32, height as f32),
         (surface_size.width as f32, surface_size.height as f32),
+        scaling_mode,
     )
     .transform
     .inversed();
@@ -477,6 +481,7 @@ pub(crate) fn create_backing_texture(
         render_texture_format,
         clear_color,
         blend_state,
+        scaling_mode,
     );
 
     let texture_format_size = texture_format_size(backing_texture_format);

src/lib.rs

@@ -55,6 +55,16 @@ struct SurfaceSize {
     height: u32,
 }
 
+/// The scaling mode controls the scaling behavior of [`renderers::ScalingRenderer`].
+#[derive(Debug, Copy, Clone)]
+pub enum ScalingMode {
+    /// The buffer is scaled up, if needed, to the nearest integer multiple of the buffer size.
+    PixelPerfect,
+    /// Fill the screen while preserving aspect ratio. The renderer effectively scales the buffer
+    /// to the nearest integer multiple first, then linearly interpolates to fit.
+    Fill,
+}
+
 /// Provides the internal state for custom shaders.
 ///
 /// A reference to this struct is given to the `render_function` closure when using
@@ -295,6 +305,23 @@ impl<'win> Pixels<'win> {
         self.context.scaling_renderer.clear_color = color;
     }
 
+    /// Set the scaling mode.
+    ///
+    /// Controls how the pixel buffer is scaled to the screen.
+    ///
+    /// ```no_run
+    /// # use pixels::{Pixels, ScalingMode};
+    /// # let window = pixels_mocks::Window;
+    /// # let surface_texture = pixels::SurfaceTexture::new(1920, 1080, &window);
+    /// let mut pixels = Pixels::new(640, 480, surface_texture)?;
+    /// // Scale the buffer up to fill the screen while preserving aspect ratio.
+    /// pixels.set_scaling_mode(ScalingMode::Fill);
+    /// # Ok::<(), pixels::Error>(())
+    /// ```
+    pub fn set_scaling_mode(&mut self, scaling_mode: ScalingMode) {
+        self.context.scaling_renderer.scaling_mode = scaling_mode;
+    }
+
     /// Returns a reference of the `wgpu` adapter used by the crate.
     ///
     /// The adapter can be used to retrieve runtime information about the host system
@@ -343,6 +370,7 @@ impl<'win> Pixels<'win> {
                 self.render_texture_format,
                 self.context.scaling_renderer.clear_color,
                 self.blend_state,
+                self.context.scaling_renderer.scaling_mode,
             )?;
 
         self.scaling_matrix_inverse = scaling_matrix_inverse;
@@ -387,6 +415,7 @@ impl<'win> Pixels<'win> {
                 self.context.texture_extent.height as f32,
             ),
             (width as f32, height as f32),
+            self.context.scaling_renderer.scaling_mode,
         )
         .transform
         .inversed();