Fix wrong gamma in WebkitGTK (#888)

Closes https://github.com/emilk/egui/issues/794

Also refactor and improve VAO support detection

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

egui_glow/src/epi_backend.rs

@@ -58,7 +58,7 @@ pub fn run(app: Box<dyn epi::App>, native_options: &epi::NativeOptions) -> ! {
         event_loop.create_proxy(),
     )));
 
-    let mut painter = crate::Painter::new(&gl, None)
+    let mut painter = crate::Painter::new(&gl, None, "")
         .map_err(|error| eprintln!("some OpenGL error occurred {}\n", error))
         .unwrap();
     let mut integration = egui_winit::epi::EpiIntegration::new(

egui_glow/src/lib.rs

@@ -123,7 +123,7 @@ impl EguiGlow {
         Self {
             egui_ctx: Default::default(),
             egui_winit: egui_winit::State::new(gl_window.window()),
-            painter: crate::Painter::new(gl, None)
+            painter: crate::Painter::new(gl, None, "")
                 .map_err(|error| {
                     eprintln!("some error occurred in initializing painter\n{}", error);
                 })

egui_glow/src/misc_util.rs

@@ -184,7 +184,8 @@ impl VAO {
     }
 }
 
-pub(crate) unsafe fn need_to_emulate_vao(gl: &glow::Context) -> bool {
+/// If returned true no need to emulate vao
+pub(crate) unsafe fn support_vao(gl: &glow::Context) -> bool {
     let web_sig = "WebGL ";
     let es_sig = "OpenGL ES ";
     let version_string = gl.get_parameter_string(glow::VERSION);
@@ -200,7 +201,7 @@ pub(crate) unsafe fn need_to_emulate_vao(gl: &glow::Context) -> bool {
             gl.supported_extensions()
                 .contains("OES_vertex_array_object")
         } else {
-            false
+            true
         }
     } else if let Some(pos) = version_string.rfind(es_sig) {
         //glow targets es2.0+ so we don't concern about OpenGL ES-CM,OpenGL ES-CL
@@ -214,7 +215,7 @@ pub(crate) unsafe fn need_to_emulate_vao(gl: &glow::Context) -> bool {
             gl.supported_extensions()
                 .contains("OES_vertex_array_object")
         } else {
-            false
+            true
         }
     } else {
         glow_debug_print(format!("detected OpenGL:{}", version_string));
@@ -225,7 +226,7 @@ pub(crate) unsafe fn need_to_emulate_vao(gl: &glow::Context) -> bool {
             gl.supported_extensions()
                 .contains("ARB_vertex_array_object")
         } else {
-            false
+            true
         }
     }
 }

egui_glow/src/painter.rs

@@ -61,18 +61,26 @@ impl Painter {
     /// Create painter.
     ///
     /// Set `pp_fb_extent` to the framebuffer size to enable `sRGB` support on OpenGL ES and WebGL.
+    /// Set `shader_prefix` if you want to turn on shader workaround e.g. `"#define EPIPHANY_WORKAROUND\n"`.
+    ///
+    /// this fix [Everything is super dark in epiphany](https://github.com/emilk/egui/issues/794)
     /// # Errors
     /// will return `Err` below cases
     /// * failed to compile shader
     /// * failed to create postprocess on webgl with `sRGB` support
     /// * failed to create buffer
-    pub fn new(gl: &glow::Context, pp_fb_extent: Option<[i32; 2]>) -> Result<Painter, String> {
-        let need_to_emulate_vao = unsafe { crate::misc_util::need_to_emulate_vao(gl) };
+    pub fn new(
+        gl: &glow::Context,
+        pp_fb_extent: Option<[i32; 2]>,
+        shader_prefix: &str,
+    ) -> Result<Painter, String> {
+        let support_vao = unsafe { crate::misc_util::support_vao(gl) };
         let shader_version = ShaderVersion::get(gl);
         let is_webgl_1 = shader_version == ShaderVersion::Es100;
         let header = shader_version.version();
         glow_debug_print(header);
         let srgb_support = gl.supported_extensions().contains("EXT_sRGB");
+
         let (post_process, srgb_support_define) = match (shader_version, srgb_support) {
             //WebGL2 support sRGB default
             (ShaderVersion::Es300, _) | (ShaderVersion::Es100, true) => unsafe {
@@ -83,7 +91,8 @@ impl Painter {
                     (
                         Some(PostProcess::new(
                             gl,
-                            need_to_emulate_vao,
+                            shader_prefix,
+                            support_vao,
                             is_webgl_1,
                             width,
                             height,
@@ -106,8 +115,9 @@ impl Painter {
                 gl,
                 glow::VERTEX_SHADER,
                 &format!(
-                    "{}\n{}\n{}",
+                    "{}\n{}\n{}\n{}",
                     header,
+                    shader_prefix,
                     shader_version.is_new_shader_interface(),
                     VERT_SRC
                 ),
@@ -116,8 +126,9 @@ impl Painter {
                 gl,
                 glow::FRAGMENT_SHADER,
                 &format!(
-                    "{}\n{}\n{}\n{}",
+                    "{}\n{}\n{}\n{}\n{}",
                     header,
+                    shader_prefix,
                     srgb_support_define,
                     shader_version.is_new_shader_interface(),
                     FRAG_SRC
@@ -136,10 +147,10 @@ impl Painter {
             let a_pos_loc = gl.get_attrib_location(program, "a_pos").unwrap();
             let a_tc_loc = gl.get_attrib_location(program, "a_tc").unwrap();
             let a_srgba_loc = gl.get_attrib_location(program, "a_srgba").unwrap();
-            let mut vertex_array = if need_to_emulate_vao {
-                crate::misc_util::VAO::emulated()
-            } else {
+            let mut vertex_array = if support_vao {
                 crate::misc_util::VAO::native(gl)
+            } else {
+                crate::misc_util::VAO::emulated()
             };
             vertex_array.bind_vertex_array(gl);
             vertex_array.bind_buffer(gl, &vertex_buffer);

egui_glow/src/post_process.rs

@@ -19,6 +19,7 @@ pub(crate) struct PostProcess {
 impl PostProcess {
     pub(crate) unsafe fn new(
         gl: &glow::Context,
+        shader_prefix: &str,
         need_to_emulate_vao: bool,
         is_webgl_1: bool,
         width: i32,
@@ -96,12 +97,20 @@ impl PostProcess {
         let vert_shader = compile_shader(
             gl,
             glow::VERTEX_SHADER,
-            include_str!("shader/post_vertex_100es.glsl"),
+            &format!(
+                "{}\n{}",
+                shader_prefix,
+                include_str!("shader/post_vertex_100es.glsl")
+            ),
         )?;
         let frag_shader = compile_shader(
             gl,
             glow::FRAGMENT_SHADER,
-            include_str!("shader/post_fragment_100es.glsl"),
+            &format!(
+                "{}\n{}",
+                shader_prefix,
+                include_str!("shader/post_fragment_100es.glsl")
+            ),
         )?;
         let program = link_program(gl, [vert_shader, frag_shader].iter())?;
 

egui_glow/src/shader/post_fragment_100es.glsl

@@ -19,4 +19,8 @@ void main() {
     gl_FragColor = texture2D(u_sampler, v_tc);
 
     gl_FragColor = srgba_from_linear(gl_FragColor) / 255.;
+    #ifdef WEBKITGTK_WORKAROUND
+    //this is better than double apply
+    gl_FragColor = vec4(pow(gl_FragColor.rgb,vec3(1.0/2.2)),gl_FragColor.a);
+    #endif
 }