X11: Use GLFW_X11_ONTHESPOT of glfwInitHint to change on-the-spot

GLFW has the function `glfwInitHint` for setting initialization parameters.
So use this instead of environmental variable.

docs/intro.dox

@@ -143,6 +143,14 @@ __GLFW_X11_XCB_VULKAN_SURFACE__ specifies whether to prefer the
 the `VK_KHR_xlib_surface` extension.  Possible values are `GLFW_TRUE` and
 `GLFW_FALSE`.  This is ignored on other platforms.
 
+@anchor GLFW_X11_ONTHESPOT_hint
+__GLFW_X11_ONTHESPOT__ specifies whether to use on-the-spot input method style.
+On X11 platform, over-the-spot style is used if this hint is `GLFW_FALSE`,
+which is the default value.  You can set `GLFW_TRUE` to use on-the-spot style
+as with other platforms.  However, on-the-spot style on X11 is unstable, so
+it is recommended not to use this hint in normal cases.  Possible values are
+`GLFW_TRUE` and `GLFW_FALSE`.  This is ignored on other platforms.  Please see
+@ref preedit for more information about IME support.
 
 @subsubsection init_hints_values Supported and default values
 
@@ -154,6 +162,7 @@ Initialization hint              | Default value                   | Supported v
 @ref GLFW_COCOA_CHDIR_RESOURCES  | `GLFW_TRUE`                     | `GLFW_TRUE` or `GLFW_FALSE`
 @ref GLFW_COCOA_MENUBAR          | `GLFW_TRUE`                     | `GLFW_TRUE` or `GLFW_FALSE`
 @ref GLFW_X11_XCB_VULKAN_SURFACE | `GLFW_TRUE`                     | `GLFW_TRUE` or `GLFW_FALSE`
+@ref GLFW_X11_ONTHESPOT          | `GLFW_FALSE`                    | `GLFW_TRUE` or `GLFW_FALSE`
 
 
 @subsection platform Runtime platform selection

include/GLFW/glfw3.h

@@ -1287,6 +1287,11 @@ extern "C" {
  *  X11 specific [init hint](@ref GLFW_X11_XCB_VULKAN_SURFACE_hint).
  */
 #define GLFW_X11_XCB_VULKAN_SURFACE 0x00052001
+/*! @brief X11 specific init hint.
+ *
+ *  X11 specific [init hint](@ref GLFW_X11_ONTHESPOT_hint).
+ */
+#define GLFW_X11_ONTHESPOT 0x00052002
 /*! @} */
 
 /*! @addtogroup init

src/init.c

@@ -61,6 +61,7 @@ static _GLFWinitconfig _glfwInitHints =
     },
     {
         GLFW_TRUE,  // X11 XCB Vulkan surface
+        GLFW_FALSE  // X11 on-the-spot IM-style
     },
 };
 
@@ -479,7 +480,10 @@ GLFWAPI void glfwInitHint(int hint, int value)
         case GLFW_X11_XCB_VULKAN_SURFACE:
             _glfwInitHints.x11.xcbVulkanSurface = value;
             return;
-    }
+        case GLFW_X11_ONTHESPOT:
+            _glfwInitHints.x11.onTheSpotIMStyle = value;
+            return;
+        }
 
     _glfwInputError(GLFW_INVALID_ENUM,
                     "Invalid init hint 0x%08X", hint);

src/internal.h

@@ -385,6 +385,7 @@ struct _GLFWinitconfig
     } ns;
     struct {
         GLFWbool  xcbVulkanSurface;
+        GLFWbool  onTheSpotIMStyle;
     } x11;
 };
 

src/x11_init.c

@@ -440,14 +440,14 @@ static GLFWbool hasUsableInputMethodStyle(void)
 {
     GLFWbool found = GLFW_FALSE;
     XIMStyles* styles = NULL;
-    const char* imStyle = getenv("IM_STYLE");
 
     if (XGetIMValues(_glfw.x11.im, XNQueryInputStyle, &styles, NULL) != NULL)
         return GLFW_FALSE;
 
-    _glfw.x11.imStyle = STYLE_OVERTHESPOT;
-    if (imStyle && strcmp(imStyle, "on-the-spot") == 0)
+    if (_glfw.hints.init.x11.onTheSpotIMStyle)
         _glfw.x11.imStyle = STYLE_ONTHESPOT;
+    else
+        _glfw.x11.imStyle = STYLE_OVERTHESPOT;
 
     for (unsigned int i = 0;  i < styles->count_styles;  i++)
     {

tests/CMakeLists.txt

@@ -32,7 +32,7 @@ add_executable(cursor cursor.c ${GLAD_GL})
 add_executable(empty WIN32 MACOSX_BUNDLE empty.c ${TINYCTHREAD} ${GLAD_GL})
 add_executable(gamma WIN32 MACOSX_BUNDLE gamma.c ${GLAD_GL})
 add_executable(icon WIN32 MACOSX_BUNDLE icon.c ${GLAD_GL})
-add_executable(input_text WIN32 MACOSX_BUNDLE input_text.c ${GLAD_GL})
+add_executable(input_text WIN32 MACOSX_BUNDLE input_text.c ${GETOPT} ${GLAD_GL})
 add_executable(inputlag WIN32 MACOSX_BUNDLE inputlag.c ${GETOPT} ${GLAD_GL})
 add_executable(joysticks WIN32 MACOSX_BUNDLE joysticks.c ${GLAD_GL})
 add_executable(tearing WIN32 MACOSX_BUNDLE tearing.c ${GLAD_GL})

tests/input_text.c

@@ -70,6 +70,8 @@
 #include <stdlib.h>
 #include <limits.h>
 
+#include "getopt.h"
+
 #if defined(FONTCONFIG_ENABLED)
     #include <fontconfig/fontconfig.h>
 #endif
@@ -103,6 +105,14 @@ static int currentIMEStatus = GLFW_FALSE;
 #define MAX_PREDIT_LEN 128
 static char preeditBuf[MAX_PREDIT_LEN] = "";
 
+void usage(void)
+{
+    printf("Usage: input_text [-h] [-s]\n");
+    printf("Options:\n");
+    printf("  -s Use on-the-spot sytle on X11. This is ignored on other platforms.\n");
+    printf("  -h Show this help\n");
+}
+
 static size_t encode_utf8(char* s, unsigned int ch)
 {
     size_t count = 0;
@@ -556,6 +566,21 @@ int main(int argc, char** argv)
     char boxBuffer[MAX_BUFFER_LEN] = "Input text here.\nここに入力してください。";
     int boxLen = strlen(boxBuffer);
     int isAutoUpdatingPreeditPosEnabled = GLFW_TRUE;
+    int ch;
+
+    while ((ch = getopt(argc, argv, "hs")) != -1)
+    {
+        switch (ch)
+        {
+            case 'h':
+                usage();
+                exit(EXIT_SUCCESS);
+
+            case 's':
+                glfwInitHint(GLFW_X11_ONTHESPOT, GLFW_TRUE);
+                break;
+        }
+    }
 
     if (!glfwInit())
         exit(EXIT_FAILURE);