Disable custom 3D painting example in the egui demo app for Es100 (#1945)

Closes https://github.com/emilk/egui/issues/1944

crates/egui_glow/src/lib.rs

@@ -19,6 +19,8 @@ mod post_process;
 mod shader_version;
 mod vao;
 
+pub use shader_version::ShaderVersion;
+
 #[cfg(all(not(target_arch = "wasm32"), feature = "winit"))]
 pub mod winit;
 #[cfg(all(not(target_arch = "wasm32"), feature = "winit"))]

crates/egui_glow/src/painter.rs

@@ -114,7 +114,7 @@ impl Painter {
 
         let shader_version = ShaderVersion::get(&gl);
         let is_webgl_1 = shader_version == ShaderVersion::Es100;
-        let header = shader_version.version();
+        let header = shader_version.version_declaration();
         tracing::debug!("Shader header: {:?}.", header);
         let srgb_support = gl.supported_extensions().contains("EXT_sRGB");
 
@@ -155,7 +155,11 @@ impl Painter {
                     "{}\n{}\n{}\n{}",
                     header,
                     shader_prefix,
-                    shader_version.is_new_shader_interface(),
+                    if shader_version.is_new_shader_interface() {
+                        "#define NEW_SHADER_INTERFACE\n"
+                    } else {
+                        ""
+                    },
                     VERT_SRC
                 ),
             )?;
@@ -167,7 +171,11 @@ impl Painter {
                     header,
                     shader_prefix,
                     srgb_support_define,
-                    shader_version.is_new_shader_interface(),
+                    if shader_version.is_new_shader_interface() {
+                        "#define NEW_SHADER_INTERFACE\n"
+                    } else {
+                        ""
+                    },
                     FRAG_SRC
                 ),
             )?;

crates/egui_glow/src/shader_version.rs

@@ -2,9 +2,10 @@
 
 use std::convert::TryInto;
 
+/// Helper for parsing and interpreting the OpenGL shader version.
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 #[allow(dead_code)]
-pub(crate) enum ShaderVersion {
+pub enum ShaderVersion {
     Gl120,
     Gl140,
     Es100,
@@ -12,7 +13,7 @@ pub(crate) enum ShaderVersion {
 }
 
 impl ShaderVersion {
-    pub(crate) fn get(gl: &glow::Context) -> Self {
+    pub fn get(gl: &glow::Context) -> Self {
         use glow::HasContext as _;
         let shading_lang_string =
             unsafe { gl.get_parameter_string(glow::SHADING_LANGUAGE_VERSION) };
@@ -52,7 +53,8 @@ impl ShaderVersion {
         }
     }
 
-    pub(crate) fn version(&self) -> &'static str {
+    /// Goes on top of the shader.
+    pub fn version_declaration(&self) -> &'static str {
         match self {
             Self::Gl120 => "#version 120\n",
             Self::Gl140 => "#version 140\n",
@@ -61,10 +63,11 @@ impl ShaderVersion {
         }
     }
 
-    pub(crate) fn is_new_shader_interface(&self) -> &'static str {
+    /// If true, use `in/out`. If `false`, use `varying` and `gl_FragColor`.
+    pub fn is_new_shader_interface(&self) -> bool {
         match self {
-            ShaderVersion::Es300 | ShaderVersion::Gl140 => "#define NEW_SHADER_INTERFACE\n",
-            _ => "",
+            Self::Gl120 | Self::Es100 => false,
+            Self::Es300 | Self::Gl140 => true,
         }
     }
 }