Make it possible to force GLES usage on Linux (#305)

Author: webbeef

src/platform/unix/wayland/connection.rs

@@ -63,7 +63,11 @@ impl Connection {
     /// Returns the OpenGL API flavor that this connection supports (OpenGL or OpenGL ES).
     #[inline]
     pub fn gl_api(&self) -> GLApi {
-        GLApi::GL
+        if std::env::var("SURFMAN_FORCE_GLES").is_ok() {
+            GLApi::GLES
+        } else {
+            GLApi::GL
+        }
     }
 
     /// Returns the "best" adapter on this system, preferring high-performance hardware adapters.

src/platform/unix/wayland/device.rs

@@ -63,6 +63,10 @@ impl Device {
     /// Returns the OpenGL API flavor that this device supports (OpenGL or OpenGL ES).
     #[inline]
     pub fn gl_api(&self) -> GLApi {
-        GLApi::GL
+        if std::env::var("SURFMAN_FORCE_GLES").is_ok() {
+            GLApi::GLES
+        } else {
+            GLApi::GL
+        }
     }
 }