allow setting the opengl version to 3

for hdr to work at least opengl3 is required.
So, now there is a feature that when enabled forces opengl3 to be used.
Once enabled every fallback to opengl2 are instead replaced by panics.

Cargo.toml

@@ -18,6 +18,7 @@ categories = ["rendering::graphics-api"]
 # Optional log-rs like macros implementation
 # disabled by default
 log-impl = []
+opengl3 = []
 
 [target.'cfg(target_os = "linux")'.dependencies]
 libc = "0.2"

src/graphics.rs

@@ -304,6 +304,7 @@ impl Error for ShaderError {
 pub enum TextureFormat {
     RGB8,
     RGBA8,
+    #[cfg(feature = "opengl3")]
     RGBA16,
     Depth,
     Alpha,
@@ -315,6 +316,7 @@ impl TextureFormat {
         match self {
             TextureFormat::RGB8 => 3 * square,
             TextureFormat::RGBA8 => 4 * square,
+            #[cfg(feature = "opengl3")]
             TextureFormat::RGBA16 => 4 * square,
             TextureFormat::Depth => 2 * square,
             TextureFormat::Alpha => 1 * square,

src/graphics/gl.rs

@@ -57,6 +57,7 @@ impl From<TextureFormat> for (GLenum, GLenum, GLenum) {
         match format {
             TextureFormat::RGB8 => (GL_RGB, GL_RGB, GL_UNSIGNED_BYTE),
             TextureFormat::RGBA8 => (GL_RGBA, GL_RGBA, GL_UNSIGNED_BYTE),
+            #[cfg(feature = "opengl3")]
             TextureFormat::RGBA16 => (GL_RGBA16F,GL_RGBA, GL_UNSIGNED_BYTE),
             TextureFormat::Depth => (GL_DEPTH_COMPONENT, GL_DEPTH_COMPONENT, GL_UNSIGNED_SHORT),
             #[cfg(target_arch = "wasm32")]

src/native/egl.rs

@@ -324,7 +324,11 @@ pub unsafe fn create_egl_context(
     if !exact_cfg_found {
         config = available_cfgs[0];
     }
-    let ctx_attributes = vec![EGL_CONTEXT_CLIENT_VERSION, 2, EGL_NONE];
+    let ctx_attributes = if cfg!(target="opengl3") {
+        vec![EGL_CONTEXT_CLIENT_VERSION, 3, EGL_NONE]
+    } else {
+        vec![EGL_CONTEXT_CLIENT_VERSION, 2, EGL_NONE]
+    };
     let context = (egl.eglCreateContext.unwrap())(
         display,
         config,

src/native/ios.rs

@@ -250,8 +250,12 @@ unsafe fn create_opengl_view(screen_rect: NSRect, _sample_count: i32, high_dpi:
     let mut eagl_context_obj: ObjcId = msg_send![eagl_context_obj, initWithAPI: 3];
     let mut gles2 = false;
     if eagl_context_obj.is_null() {
-        eagl_context_obj = msg_send![eagl_context_obj, initWithAPI: 2];
-        gles2 = true;
+        if cfg!(target = "opengl3") {
+            panic!("unsupported opengl version")
+        } else {
+            eagl_context_obj = msg_send![eagl_context_obj, initWithAPI: 2];
+            gles2 = true;
+        }
     }
 
     msg_send_![

src/native/linux_x11/glx.rs

@@ -311,16 +311,29 @@ impl Glx {
         }
 
         // _sapp_x11_grab_error_handler(libx11);
-        let attribs: [libc::c_int; 8] = [
-            GLX_CONTEXT_MAJOR_VERSION_ARB,
-            2,
-            GLX_CONTEXT_MINOR_VERSION_ARB,
-            1,
-            GLX_CONTEXT_FLAGS_ARB,
-            GLX_CONTEXT_CORE_PROFILE_BIT_ARB,
-            0,
-            0,
-        ];
+        let attribs: [libc::c_int; 8] = if(cfg!(feature="opengl3")){
+            [
+                GLX_CONTEXT_MAJOR_VERSION_ARB,
+                3,
+                GLX_CONTEXT_MINOR_VERSION_ARB,
+                1,
+                GLX_CONTEXT_FLAGS_ARB,
+                GLX_CONTEXT_CORE_PROFILE_BIT_ARB,
+                0,
+                0,
+            ]
+        } else {
+            [
+                GLX_CONTEXT_MAJOR_VERSION_ARB,
+                2,
+                GLX_CONTEXT_MINOR_VERSION_ARB,
+                1,
+                GLX_CONTEXT_FLAGS_ARB,
+                GLX_CONTEXT_CORE_PROFILE_BIT_ARB,
+                0,
+                0,
+            ]
+        };
         let glx_ctx = self.extensions.glxCreateContextAttribsARB.unwrap()(
             display,
             self.fbconfig,