EGL: Add better errors for client API mismatch

Because EGL ties client API support to configs, attempts to create
a context with an unavailable client API will fail with the unhelpful
"failed to find suitable config" error description.

This attempts to detect cases where there are usable configs for the
other client API and emit a hopefully more helpful error.

Related to #2173

src/egl_context.c

@@ -94,7 +94,18 @@ static GLFWbool chooseEGLConfig(const _GLFWctxconfig* ctxconfig,
     EGLConfig* nativeConfigs;
     _GLFWfbconfig* usableConfigs;
     const _GLFWfbconfig* closest;
-    int i, nativeCount, usableCount;
+    int i, nativeCount, usableCount, apiBit;
+    GLFWbool wrongApiAvailable = GLFW_FALSE;
+
+    if (ctxconfig->client == GLFW_OPENGL_ES_API)
+    {
+        if (ctxconfig->major == 1)
+            apiBit = EGL_OPENGL_ES_BIT;
+        else
+            apiBit = EGL_OPENGL_ES2_BIT;
+    }
+    else
+        apiBit = EGL_OPENGL_BIT;
 
     eglGetConfigs(_glfw.egl.display, NULL, 0, &nativeCount);
     if (!nativeCount)
@@ -146,23 +157,10 @@ static GLFWbool chooseEGLConfig(const _GLFWctxconfig* ctxconfig,
         }
 #endif // _GLFW_X11
 
-        if (ctxconfig->client == GLFW_OPENGL_ES_API)
+        if (!(getEGLConfigAttrib(n, EGL_RENDERABLE_TYPE) & apiBit))
-        {
-            if (ctxconfig->major == 1)
-            {
-                if (!(getEGLConfigAttrib(n, EGL_RENDERABLE_TYPE) & EGL_OPENGL_ES_BIT))
-                    continue;
-            }
-            else
-            {
-                if (!(getEGLConfigAttrib(n, EGL_RENDERABLE_TYPE) & EGL_OPENGL_ES2_BIT))
-                    continue;
-            }
-        }
-        else if (ctxconfig->client == GLFW_OPENGL_API)
         {
-            if (!(getEGLConfigAttrib(n, EGL_RENDERABLE_TYPE) & EGL_OPENGL_BIT))
+            wrongApiAvailable = GLFW_TRUE;
-                continue;
+            continue;
         }
 
         u->redBits = getEGLConfigAttrib(n, EGL_RED_SIZE);
@@ -198,6 +196,35 @@ static GLFWbool chooseEGLConfig(const _GLFWctxconfig* ctxconfig,
     closest = _glfwChooseFBConfig(desired, usableConfigs, usableCount);
     if (closest)
         *result = (EGLConfig) closest->handle;
+    else
+    {
+        if (wrongApiAvailable)
+        {
+            if (ctxconfig->client == GLFW_OPENGL_ES_API)
+            {
+                if (ctxconfig->major == 1)
+                {
+                    _glfwInputError(GLFW_API_UNAVAILABLE,
+                                    "EGL: Failed to find support for OpenGL ES 1.x");
+                }
+                else
+                {
+                    _glfwInputError(GLFW_API_UNAVAILABLE,
+                                    "EGL: Failed to find support for OpenGL ES 2 or later");
+                }
+            }
+            else
+            {
+                _glfwInputError(GLFW_API_UNAVAILABLE,
+                                "EGL: Failed to find support for OpenGL");
+            }
+        }
+        else
+        {
+            _glfwInputError(GLFW_FORMAT_UNAVAILABLE,
+                            "EGL: Failed to find a suitable EGLConfig");
+        }
+    }
 
     _glfw_free(nativeConfigs);
     _glfw_free(usableConfigs);
@@ -550,11 +577,7 @@ GLFWbool _glfwCreateContextEGL(_GLFWwindow* window,
         share = ctxconfig->share->context.egl.handle;
 
     if (!chooseEGLConfig(ctxconfig, fbconfig, &config))
-    {
-        _glfwInputError(GLFW_FORMAT_UNAVAILABLE,
-                        "EGL: Failed to find a suitable EGLConfig");
         return GLFW_FALSE;
-    }
 
     if (ctxconfig->client == GLFW_OPENGL_ES_API)
     {
@@ -815,11 +838,7 @@ GLFWbool _glfwChooseVisualEGL(const _GLFWwndconfig* wndconfig,
     const long vimask = VisualScreenMask | VisualIDMask;
 
     if (!chooseEGLConfig(ctxconfig, fbconfig, &native))
-    {
-        _glfwInputError(GLFW_FORMAT_UNAVAILABLE,
-                        "EGL: Failed to find a suitable EGLConfig");
         return GLFW_FALSE;
-    }
 
     eglGetConfigAttrib(_glfw.egl.display, native,
                        EGL_NATIVE_VISUAL_ID, &visualID);