gtk,opengl: cleanup & fixes for #14052 (#14279)

Fixes most issues mentioned in #14243, #14254 and elsewhere e.g. on
Discord. Will add more fixes if they can be solidly reproduced.

Please review each commit individually.

passthrough.glsl

@@ -0,0 +1,4 @@
+void mainImage(out vec4 fragColor, in vec2 fragCoord) {
+    vec2 uv = fragCoord / iResolution.xy;
+    fragColor = vec4(texture(iChannel0, uv).rgb, 1.0);
+}

pkg/opengl/Sampler.zig

@@ -27,13 +27,22 @@ pub fn parameter(
     comptime name: Texture.Parameter,
     value: name.Type(),
 ) errors.Error!void {
-    switch (@TypeOf(value)) {
+    const T = name.Type();
+
+    switch (T) {
         c.GLint => glad.context.SamplerParameteri.?(
             self.id,
             @intFromEnum(name),
             value,
         ),
-        else => unreachable,
+        else => switch (@typeInfo(T)) {
+            .@"enum" => glad.context.SamplerParameteri.?(
+                self.id,
+                @intFromEnum(name),
+                @intFromEnum(value),
+            ),
+            else => @compileLog("unsupported parameter type", T),
+        },
     }
     try errors.getError();
 }

src/apprt/gtk/class/application.zig

@@ -3376,32 +3376,23 @@ const Action = struct {
 fn setGtkEnv(config: *const CoreConfig) std.Io.Writer.Error!void {
     assert(gtk.isInitialized() == 0);
 
-    var gdk_debug: struct {
-        /// output OpenGL debug information
+    const gdk_debug: struct {
+        /// Output OpenGL debug information,
+        /// `gtk-opengl-debug` dumps logs directly to stderr so both must be true
+        /// to enable OpenGL debugging.
         opengl: bool = false,
-        // GTK's new renderer can cause blurry font when using fractional scaling.
-        @"gl-no-fractional": bool = false,
     } = .{
-        // `gtk-opengl-debug` dumps logs directly to stderr so both must be true
-        // to enable OpenGL debugging.
         .opengl = global.logging().stderr and config.@"gtk-opengl-debug",
     };
 
-    var gdk_disable: struct {
-        /// current gtk implementation for color management is not good enough.
-        /// see: https://bugs.kde.org/show_bug.cgi?id=495647
-        /// gtk issue: https://gitlab.gnome.org/GNOME/gtk/-/issues/6864
-        @"color-mgmt": bool = true,
+    const gdk_disable: struct {
+        // Even though we don't use GTK's GL context anymore, there can still
+        // occasionally be conflicts when Vulkan and OpenGL are used together.
+        // Disabling Vulkan also saves hundreds of milliseconds of initialization
+        // time on certain systems.
+        vulkan: bool = true,
     } = .{};
 
-    if (gtk_version.runtimeAtLeast(4, 18, 0)) {
-        gdk_disable.@"color-mgmt" = false;
-    }
-    if (gtk_version.runtimeUntil(4, 17, 5)) {
-        // Removed at GTK v4.17.5
-        gdk_debug.@"gl-no-fractional" = true;
-    }
-
     {
         var buf: [1024]u8 = undefined;
         var writer: std.Io.Writer = .fixed(&buf);

src/apprt/gtk/class/imgui_widget.zig

@@ -317,9 +317,6 @@ pub const ImguiWidget = extern struct {
             cimgui.c.ImGui_Render();
         }
 
-        // OpenGL final render
-        gl.clearColor(0x28 / 0xFF, 0x2C / 0xFF, 0x34 / 0xFF, 1.0);
-        gl.clear(gl.c.GL_COLOR_BUFFER_BIT);
         cimgui.ImGui_ImplOpenGL3_RenderDrawData(cimgui.c.ImGui_GetDrawData());
 
         return @intFromBool(true);

src/renderer/OpenGL.zig

@@ -59,12 +59,16 @@ pub fn init(alloc: Allocator, opts: rendererpkg.Options) !OpenGL {
     // Choose a config. We need a config that is renderable with
     // OpenGL and a RGBA8 color buffer.
     const config = egl.Config.choose(display, &.{
+        // EGL_SURFACE_TYPE defaults to EGL_WINDOW_BIT even though
+        // we are rendering exclusively through surfaceless mode.
+        // This is no problem on Mesa but we need to specify this
+        // explicitly for proprietary Nvidia drivers.
+        egl.c.EGL_SURFACE_TYPE,    0,
         egl.c.EGL_RENDERABLE_TYPE, egl.c.EGL_OPENGL_BIT,
         egl.c.EGL_RED_SIZE,        8,
         egl.c.EGL_GREEN_SIZE,      8,
         egl.c.EGL_BLUE_SIZE,       8,
         egl.c.EGL_ALPHA_SIZE,      8,
-        egl.c.EGL_NONE,
     }) catch |err| {
         log.warn("failed to choose config err={}", .{err});
         return err;
@@ -75,7 +79,6 @@ pub fn init(alloc: Allocator, opts: rendererpkg.Options) !OpenGL {
         egl.c.EGL_CONTEXT_MAJOR_VERSION,       MIN_VERSION_MAJOR,
         egl.c.EGL_CONTEXT_MINOR_VERSION,       MIN_VERSION_MINOR,
         egl.c.EGL_CONTEXT_OPENGL_PROFILE_MASK, egl.c.EGL_CONTEXT_OPENGL_CORE_PROFILE_BIT,
-        egl.c.EGL_NONE,
     }) catch |err| {
         log.warn("failed to create EGL context err={}", .{err});
         return err;