Add support for mipmap textures. (emilk#5146)

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Adds support for mipmaps in the `glow` backend.

Should be possible to implement for `wgpu` in the future as well, but
requires a custom compute kernel.

crates/egui_glow/src/painter.rs

@@ -22,14 +22,18 @@ const VERT_SRC: &str = include_str!("shader/vertex.glsl");
 const FRAG_SRC: &str = include_str!("shader/fragment.glsl");
 
 trait TextureFilterExt {
-    fn glow_code(&self) -> u32;
+    fn glow_code(&self, mipmap: Option<egui::TextureFilter>) -> u32;
 }
 
 impl TextureFilterExt for egui::TextureFilter {
-    fn glow_code(&self) -> u32 {
-        match self {
-            Self::Linear => glow::LINEAR,
-            Self::Nearest => glow::NEAREST,
+    fn glow_code(&self, mipmap: Option<egui::TextureFilter>) -> u32 {
+        match (self, mipmap) {
+            (Self::Linear, None) => glow::LINEAR,
+            (Self::Nearest, None) => glow::NEAREST,
+            (Self::Linear, Some(Self::Linear)) => glow::LINEAR_MIPMAP_LINEAR,
+            (Self::Nearest, Some(Self::Linear)) => glow::NEAREST_MIPMAP_LINEAR,
+            (Self::Linear, Some(Self::Nearest)) => glow::LINEAR_MIPMAP_NEAREST,
+            (Self::Nearest, Some(Self::Nearest)) => glow::NEAREST_MIPMAP_NEAREST,
         }
     }
 }
@@ -569,12 +573,12 @@ impl Painter {
             self.gl.tex_parameter_i32(
                 glow::TEXTURE_2D,
                 glow::TEXTURE_MAG_FILTER,
-                options.magnification.glow_code() as i32,
+                options.magnification.glow_code(None) as i32,
             );
             self.gl.tex_parameter_i32(
                 glow::TEXTURE_2D,
                 glow::TEXTURE_MIN_FILTER,
-                options.minification.glow_code() as i32,
+                options.minification.glow_code(options.mipmap_mode) as i32,
             );
 
             self.gl.tex_parameter_i32(
@@ -635,6 +639,11 @@ impl Painter {
                 );
                 check_for_gl_error!(&self.gl, "tex_image_2d");
             }
+
+            if options.mipmap_mode.is_some() {
+                self.gl.generate_mipmap(glow::TEXTURE_2D);
+                check_for_gl_error!(&self.gl, "generate_mipmap");
+            }
         }
     }
 

crates/epaint/src/textures.rs

@@ -159,6 +159,16 @@ pub struct TextureOptions {
 
     /// How to wrap the texture when the texture coordinates are outside the [0, 1] range.
     pub wrap_mode: TextureWrapMode,
+
+    /// How to filter between texture mipmaps.
+    ///
+    /// Mipmaps ensures textures look smooth even when the texture is very small and pixels are much
+    /// larger than individual texels.
+    ///
+    /// # Notes
+    ///
+    /// - This may not be available on all backends (currently only `egui_glow`).
+    pub mipmap_mode: Option<TextureFilter>,
 }
 
 impl TextureOptions {
@@ -167,42 +177,55 @@ impl TextureOptions {
         magnification: TextureFilter::Linear,
         minification: TextureFilter::Linear,
         wrap_mode: TextureWrapMode::ClampToEdge,
+        mipmap_mode: None,
     };
 
     /// Nearest magnification and minification.
     pub const NEAREST: Self = Self {
         magnification: TextureFilter::Nearest,
         minification: TextureFilter::Nearest,
         wrap_mode: TextureWrapMode::ClampToEdge,
+        mipmap_mode: None,
     };
 
     /// Linear magnification and minification, but with the texture repeated.
     pub const LINEAR_REPEAT: Self = Self {
         magnification: TextureFilter::Linear,
         minification: TextureFilter::Linear,
         wrap_mode: TextureWrapMode::Repeat,
+        mipmap_mode: None,
     };
 
     /// Linear magnification and minification, but with the texture mirrored and repeated.
     pub const LINEAR_MIRRORED_REPEAT: Self = Self {
         magnification: TextureFilter::Linear,
         minification: TextureFilter::Linear,
         wrap_mode: TextureWrapMode::MirroredRepeat,
+        mipmap_mode: None,
     };
 
     /// Nearest magnification and minification, but with the texture repeated.
     pub const NEAREST_REPEAT: Self = Self {
         magnification: TextureFilter::Nearest,
         minification: TextureFilter::Nearest,
         wrap_mode: TextureWrapMode::Repeat,
+        mipmap_mode: None,
     };
 
     /// Nearest magnification and minification, but with the texture mirrored and repeated.
     pub const NEAREST_MIRRORED_REPEAT: Self = Self {
         magnification: TextureFilter::Nearest,
         minification: TextureFilter::Nearest,
         wrap_mode: TextureWrapMode::MirroredRepeat,
+        mipmap_mode: None,
     };
+
+    pub const fn with_mipmap_mode(self, mipmap_mode: Option<TextureFilter>) -> Self {
+        Self {
+            mipmap_mode,
+            ..self
+        }
+    }
 }
 
 impl Default for TextureOptions {