egui_glow: Add function to set the texture filter (#1041)

* Allow setting the scale filter for `glow` backend

This commit adds a `set_scale_filter` method to the `glow` painter so that
textures can be set to scale using nearest-neighbour scaling rather than
linear. This is useful for pixel art.

I wasn't entirely sure what kind of API you want for this kind of change so I
went with what seemed least intrusive, I don't mind doing something more
holistic if this isn't what you had in mind.

* Rename scale_filter -> texture_filter

* Store the TextureFilter directly

* PR link in changelog

* Use inter-doc links

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

egui_glow/CHANGELOG.md

@@ -3,7 +3,7 @@ All notable changes to the `egui_glow` integration will be noted in this file.
 
 
 ## Unreleased
-
+* Added `set_texture_filter` method to `Painter` ((#1041)[https://github.com/emilk/egui/pull/1041]).
 
 ## 0.16.0 - 2021-12-29
 * Made winit/glutin an optional dependency ([#868](https://github.com/emilk/egui/pull/868)).

egui_glow/src/misc_util.rs

@@ -2,10 +2,13 @@
 use glow::HasContext;
 use std::option::Option::Some;
 
+use crate::painter::TextureFilter;
+
 pub(crate) fn srgbtexture2d(
     gl: &glow::Context,
     is_webgl_1: bool,
     srgb_support: bool,
+    texture_filter: TextureFilter,
     data: &[u8],
     w: usize,
     h: usize,
@@ -20,12 +23,12 @@ pub(crate) fn srgbtexture2d(
         gl.tex_parameter_i32(
             glow::TEXTURE_2D,
             glow::TEXTURE_MAG_FILTER,
-            glow::LINEAR as i32,
+            texture_filter.glow_code() as i32,
         );
         gl.tex_parameter_i32(
             glow::TEXTURE_2D,
             glow::TEXTURE_MIN_FILTER,
-            glow::LINEAR as i32,
+            texture_filter.glow_code() as i32,
         );
         gl.tex_parameter_i32(
             glow::TEXTURE_2D,

egui_glow/src/painter.rs

@@ -35,6 +35,8 @@ pub struct Painter {
     is_embedded: bool,
     vertex_array: crate::misc_util::VAO,
     srgb_support: bool,
+    /// The filter used for subsequent textures.
+    texture_filter: TextureFilter,
     post_process: Option<PostProcess>,
     vertex_buffer: glow::Buffer,
     element_array_buffer: glow::Buffer,
@@ -52,6 +54,27 @@ pub struct Painter {
     destroyed: bool,
 }
 
+#[derive(Copy, Clone)]
+pub enum TextureFilter {
+    Linear,
+    Nearest,
+}
+
+impl Default for TextureFilter {
+    fn default() -> Self {
+        TextureFilter::Linear
+    }
+}
+
+impl TextureFilter {
+    pub(crate) fn glow_code(&self) -> u32 {
+        match self {
+            TextureFilter::Linear => glow::LINEAR,
+            TextureFilter::Nearest => glow::NEAREST,
+        }
+    }
+}
+
 impl Painter {
     /// Create painter.
     ///
@@ -190,6 +213,7 @@ impl Painter {
                 is_embedded: matches!(shader_version, ShaderVersion::Es100 | ShaderVersion::Es300),
                 vertex_array,
                 srgb_support,
+                texture_filter: Default::default(),
                 post_process,
                 vertex_buffer,
                 element_array_buffer,
@@ -224,6 +248,7 @@ impl Painter {
                 gl,
                 self.is_webgl_1,
                 self.srgb_support,
+                self.texture_filter,
                 &pixels,
                 font_image.width,
                 font_image.height,
@@ -387,6 +412,12 @@ impl Painter {
         }
     }
 
+    // Set the filter to be used for any subsequent textures loaded via
+    // [`Self::set_texture`].
+    pub fn set_texture_filter(&mut self, texture_filter: TextureFilter) {
+        self.texture_filter = texture_filter;
+    }
+
     // ------------------------------------------------------------------------
 
     #[cfg(feature = "epi")]
@@ -410,6 +441,7 @@ impl Painter {
             gl,
             self.is_webgl_1,
             self.srgb_support,
+            self.texture_filter,
             &pixels,
             image.size[0],
             image.size[1],