From d7b96a424fdd939aa7de65153e3b9baa20edf626 Mon Sep 17 00:00:00 2001
From: Michael Lutz <michi@icosahedron.de>
Date: Sat, 16 Jan 2021 16:43:05 +0100
Subject: Codechange: [OpenGL] Use new-style extension testing introduced with
 OpenGL 3.0.

---
 src/video/opengl.cpp  | 36 +++++++++++++++++++++++++++++++++---
 src/video/opengl.h    |  9 +++++++--
 src/video/win32_v.cpp |  8 +++++++-
 3 files changed, 47 insertions(+), 6 deletions(-)

(limited to 'src')

diff --git a/src/video/opengl.cpp b/src/video/opengl.cpp
index 4d759e60f..c811be2ef 100644
--- a/src/video/opengl.cpp
+++ b/src/video/opengl.cpp
@@ -32,6 +32,8 @@
 
 /* static */ OpenGLBackend *OpenGLBackend::instance = nullptr;
 
+GetOGLProcAddressProc GetOGLProcAddress;
+
 /**
  * Find a substring in a string made of space delimited elements. The substring
  * has to match the complete element, partial matches don't count.
@@ -65,7 +67,31 @@ static const char *FindStringInExtensionList(const char *string, const char *sub
  */
 static bool IsOpenGLExtensionSupported(const char *extension)
 {
-	return FindStringInExtensionList((const char *)glGetString(GL_EXTENSIONS), extension) != nullptr;
+	static PFNGLGETSTRINGIPROC glGetStringi = nullptr;
+	static bool glGetStringi_loaded = false;
+
+	/* Starting with OpenGL 3.0 the preferred API to get the extensions
+	 * has changed. Try to load the required function once. */
+	if (!glGetStringi_loaded) {
+		if (IsOpenGLVersionAtLeast(3, 0)) glGetStringi = (PFNGLGETSTRINGIPROC)GetOGLProcAddress("glGetStringi");
+		glGetStringi_loaded = true;
+	}
+
+	if (glGetStringi != nullptr) {
+		/* New style: Each supported extension can be queried and compared independently. */
+		GLint num_exts;
+		glGetIntegerv(GL_NUM_EXTENSIONS, &num_exts);
+
+		for (GLint i = 0; i < num_exts; i++) {
+			const char *entry = (const char *)glGetStringi(GL_EXTENSIONS, i);
+			if (strcmp(entry, extension) == 0) return true;
+		}
+	} else {
+		/* Old style: A single, space-delimited string for all extensions. */
+		return FindStringInExtensionList((const char *)glGetString(GL_EXTENSIONS), extension) != nullptr;
+	}
+
+	return false;
 }
 
 static byte _gl_major_ver = 0; ///< Major OpenGL version.
@@ -78,7 +104,7 @@ static byte _gl_minor_ver = 0; ///< Minor OpenGL version.
  * @pre OpenGL was initialized.
  * @return True if the OpenGL version is equal or higher than the requested one.
  */
-static bool IsOpenGLVersionAtLeast(byte major, byte minor)
+bool IsOpenGLVersionAtLeast(byte major, byte minor)
 {
 	return (_gl_major_ver > major) || (_gl_major_ver == major && _gl_minor_ver >= minor);
 }
@@ -86,11 +112,15 @@ static bool IsOpenGLVersionAtLeast(byte major, byte minor)
 
 /**
  * Create and initialize the singleton back-end class.
+ * @param get_proc Callback to get an OpenGL function from the OS driver.
+ * @return nullptr on success, error message otherwise.
  */
-/* static */ const char *OpenGLBackend::Create()
+/* static */ const char *OpenGLBackend::Create(GetOGLProcAddressProc get_proc)
 {
 	if (OpenGLBackend::instance != nullptr) OpenGLBackend::Destroy();
 
+	GetOGLProcAddress = get_proc;
+
 	OpenGLBackend::instance = new OpenGLBackend();
 	return OpenGLBackend::instance->Init();
 }
diff --git a/src/video/opengl.h b/src/video/opengl.h
index 9db1be5f5..08ef56b9a 100644
--- a/src/video/opengl.h
+++ b/src/video/opengl.h
@@ -14,7 +14,12 @@
 
 #include "../core/alloc_type.hpp"
 
-/** Platform-independent back-end singleton class for OpenGL video drivers. */
+typedef void (*OGLProc)();
+typedef OGLProc (*GetOGLProcAddressProc)(const char *proc);
+
+bool IsOpenGLVersionAtLeast(byte major, byte minor);
+
+/** Platform-independent back-end class for OpenGL video drivers. */
 class OpenGLBackend : public ZeroedMemoryAllocator {
 private:
 	static OpenGLBackend *instance; ///< Singleton instance pointer.
@@ -33,7 +38,7 @@ public:
 	{
 		return OpenGLBackend::instance;
 	}
-	static const char *Create();
+	static const char *Create(GetOGLProcAddressProc get_proc);
 	static void Destroy();
 
 	bool Resize(int w, int h, bool force = false);
diff --git a/src/video/win32_v.cpp b/src/video/win32_v.cpp
index c97dccf44..ddfe365f7 100644
--- a/src/video/win32_v.cpp
+++ b/src/video/win32_v.cpp
@@ -1331,6 +1331,12 @@ void VideoDriver_Win32GDI::PaintThread()
 #	define PFD_SUPPORT_COMPOSITION 0x00008000
 #endif
 
+/** Platform-specific callback to get an OpenGL funtion pointer. */
+static OGLProc GetOGLProcAddressCallback(const char *proc)
+{
+	return reinterpret_cast<OGLProc>(wglGetProcAddress(proc));
+}
+
 static FVideoDriver_Win32OpenGL iFVideoDriver_Win32OpenGL;
 
 const char *VideoDriver_Win32OpenGL::Start(const StringList &param)
@@ -1412,7 +1418,7 @@ const char *VideoDriver_Win32OpenGL::AllocateContext()
 	if (this->gl_rc == 0) return "Can't create OpenGL context";
 	if (!wglMakeCurrent(this->dc, this->gl_rc)) return "Can't active GL context";
 
-	return OpenGLBackend::Create();
+	return OpenGLBackend::Create(&GetOGLProcAddressCallback);
 }
 
 bool VideoDriver_Win32OpenGL::ToggleFullscreen(bool full_screen)
-- 
cgit v1.2.3-70-g09d2