Feature: [SDL2] OpenGL support

src/video/sdl2_opengl_v.h

@@ -0,0 +1,52 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file sdl2_opengl_v.h OpenGL backend of the SDL2 video driver. */
+
+#include "sdl2_v.h"
+
+/** The OpenGL video driver for windows. */
+class VideoDriver_SDL_OpenGL : public VideoDriver_SDL {
+public:
+	VideoDriver_SDL_OpenGL() : gl_context(nullptr), anim_buffer(nullptr) {}
+
+	const char *Start(const StringList &param) override;
+
+	void Stop() override;
+
+	bool HasEfficient8Bpp() const override { return true; }
+
+	bool UseSystemCursor() override { return true; }
+
+	void ClearSystemSprites() override;
+
+	bool HasAnimBuffer() override { return true; }
+	uint8 *GetAnimBuffer() override { return this->anim_buffer; }
+
+	const char *GetName() const override { return "sdl-opengl"; }
+
+protected:
+	bool AllocateBackingStore(int w, int h, bool force = false) override;
+	void *GetVideoPointer() override;
+	void ReleaseVideoPointer() override;
+	void Paint() override;
+	bool CreateMainWindow(uint w, uint h, uint flags) override;
+
+private:
+	void  *gl_context;  ///< OpenGL context.
+	uint8 *anim_buffer; ///< Animation buffer from OpenGL back-end.
+
+	const char *AllocateContext();
+	void DestroyContext();
+};
+
+/** The factory for SDL' OpenGL video driver. */
+class FVideoDriver_SDL_OpenGL : public DriverFactoryBase {
+public:
+	FVideoDriver_SDL_OpenGL() : DriverFactoryBase(Driver::DT_VIDEO, 8, "sdl-opengl", "SDL OpenGL Video Driver") {}
+	/* virtual */ Driver *CreateInstance() const override { return new VideoDriver_SDL_OpenGL(); }
+};