Codechange: [OpenGL] Use a pixel buffer object to store the video buffer.

4 files changed, 87 insertions, 33 deletions

diff --git a/src/video/opengl.cpp b/src/video/opengl.cpp
index 6f329994f..cbad8a167 100644
--- a/src/video/opengl.cpp
+++ b/src/video/opengl.cpp
@@ -264,9 +264,9 @@ OpenGLBackend::~OpenGLBackend()
 	if (_glDeleteVertexArrays != nullptr) _glDeleteVertexArrays(1, &this->vao_quad);
 	if (_glDeleteBuffers != nullptr) {
 		_glDeleteBuffers(1, &this->vbo_quad);
+		_glDeleteBuffers(1, &this->vid_pbo);
 	}
 	glDeleteTextures(1, &this->vid_texture);
-	free(this->vid_buffer);
 }
 
 /**
@@ -297,6 +297,8 @@ const char *OpenGLBackend::Init()
 	/* Check for vertex buffer objects. */
 	if (!IsOpenGLVersionAtLeast(1, 5) && !IsOpenGLExtensionSupported("ARB_vertex_buffer_object")) return "Vertex buffer objects not supported";
 	if (!BindVBOExtension()) return "Failed to bind VBO extension functions";
+	/* Check for pixel buffer objects. */
+	if (!IsOpenGLVersionAtLeast(2, 1) && !IsOpenGLExtensionSupported("GL_ARB_pixel_buffer_object")) return "Pixel buffer objects not supported";
 	/* Check for vertex array objects. */
 	if (!IsOpenGLVersionAtLeast(3, 0) && (!IsOpenGLExtensionSupported("GL_ARB_vertex_array_object") || !IsOpenGLExtensionSupported("GL_APPLE_vertex_array_object"))) return "Vertex array objects not supported";
 	if (!BindVBAExtension()) return "Failed to bind VBA extension functions";
@@ -312,6 +314,11 @@ const char *OpenGLBackend::Init()
 	glBindTexture(GL_TEXTURE_2D, 0);
 	if (glGetError() != GL_NO_ERROR) return "Can't generate video buffer texture";
 
+	/* Create pixel buffer object as video buffer storage. */
+	_glGenBuffers(1, &this->vid_pbo);
+	_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, this->vid_pbo);
+	if (glGetError() != GL_NO_ERROR) return "Can't allocate pixel buffer for video buffer";
+
 	/* Prime vertex buffer with a full-screen quad and store
 	 * the corresponding state in a vertex array object. */
 	static const Simple2DVertex vert_array[] = {
@@ -355,13 +362,14 @@ const char *OpenGLBackend::Init()
  */
 bool OpenGLBackend::Resize(int w, int h, bool force)
 {
-	if (!force && _screen.width == w && _screen.height == h && this->vid_buffer != nullptr) return false;
+	if (!force && _screen.width == w && _screen.height == h) return false;
 
 	glViewport(0, 0, w, h);
 
-	/* Re-allocate video buffer texture. */
-	free(this->vid_buffer);
-	this->vid_buffer = CallocT<uint32>(w * h); // 32bpp
+	/* Re-allocate video buffer texture and backing store. */
+	_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, this->vid_pbo);
+	_glBufferData(GL_PIXEL_UNPACK_BUFFER, w * h * 4, nullptr, GL_DYNAMIC_READ); // Buffer content has to persist from frame to frame and is read back by the blitter, which means a READ usage hint.
+	_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
 
 	glBindTexture(GL_TEXTURE_2D, this->vid_texture);
 	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, w, h, 0, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV, nullptr);
@@ -371,30 +379,50 @@ bool OpenGLBackend::Resize(int w, int h, bool force)
 	_screen.height = h;
 	_screen.width = w;
 	_screen.pitch = w;
-	_screen.dst_ptr = this->GetVideoBuffer();
+	_screen.dst_ptr = nullptr;
 
 	return true;
 }
 
 /**
  * Render video buffer to the screen.
+ */
+void OpenGLBackend::Paint()
+{
+	glClear(GL_COLOR_BUFFER_BIT);
+
+	/* Blit video buffer to screen. */
+	glBindTexture(GL_TEXTURE_2D, this->vid_texture);
+	_glBindVertexArray(this->vao_quad);
+	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+}
+
+/**
+ * Get a pointer to the memory for the video driver to draw to.
+ * @return Pointer to draw on.
+ */
+void *OpenGLBackend::GetVideoBuffer()
+{
+	_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, this->vid_pbo);
+	return _glMapBuffer(GL_PIXEL_UNPACK_BUFFER, GL_READ_WRITE);
+}
+
+/**
+ * Update video buffer texture after the video buffer was filled.
  * @param update_rect Rectangle encompassing the dirty region of the video buffer.
  */
-void OpenGLBackend::Paint(Rect update_rect)
+void OpenGLBackend::ReleaseVideoBuffer(const Rect &update_rect)
 {
-	assert(this->vid_buffer != nullptr);
+	assert(this->vid_pbo != 0);
 
-	glClear(GL_COLOR_BUFFER_BIT);
+	_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, this->vid_pbo);
+	_glUnmapBuffer(GL_PIXEL_UNPACK_BUFFER);
 
 	/* Update changed rect of the video buffer texture. */
-	glBindTexture(GL_TEXTURE_2D, this->vid_texture);
 	if (!IsEmptyRect(update_rect)) {
+		glBindTexture(GL_TEXTURE_2D, this->vid_texture);
 		glPixelStorei(GL_UNPACK_ROW_LENGTH, _screen.pitch);
-		glTexSubImage2D(GL_TEXTURE_2D, 0, update_rect.left, update_rect.top, update_rect.right - update_rect.left, update_rect.bottom - update_rect.top, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV, (uint32 *)this->vid_buffer + update_rect.top * _screen.pitch + update_rect.left);
+		glTexSubImage2D(GL_TEXTURE_2D, 0, update_rect.left, update_rect.top, update_rect.right - update_rect.left, update_rect.bottom - update_rect.top, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV, (GLvoid *)(size_t)(update_rect.top * _screen.pitch * 4 + update_rect.left * 4));
 	}
-
-	/* Blit video buffer to screen. */
-	_glBindVertexArray(this->vao_quad);
-	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
 
diff --git a/src/video/opengl.h b/src/video/opengl.h
index dfc71b5f7..16d72ff87 100644
--- a/src/video/opengl.h
+++ b/src/video/opengl.h
@@ -25,7 +25,7 @@ class OpenGLBackend : public ZeroedMemoryAllocator {
 private:
 	static OpenGLBackend *instance; ///< Singleton instance pointer.
 
-	void *vid_buffer;   ///< Pointer to the memory used for the video driver to draw to.
+	GLuint vid_pbo;     ///< Pixel buffer object storing the memory used for the video driver to draw to.
 	GLuint vid_texture; ///< Texture handle for the video buffer texture.
 	GLuint vao_quad;    ///< Vertex array object storing the rendering state for the fullscreen quad.
 	GLuint vbo_quad;    ///< Vertex buffer with a fullscreen quad.
@@ -45,13 +45,10 @@ public:
 	static void Destroy();
 
 	bool Resize(int w, int h, bool force = false);
-	void Paint(Rect update_rect);
+	void Paint();
 
-	/**
-	 * Get a pointer to the memory for the video driver to draw to.
-	 * @return Pointer to draw on.
-	 */
-	void *GetVideoBuffer() { return this->vid_buffer; }
+	void *GetVideoBuffer();
+	void ReleaseVideoBuffer(const Rect &update_rect);
 };
 
 #endif /* VIDEO_OPENGL_H */
diff --git a/src/video/win32_v.cpp b/src/video/win32_v.cpp
index 0e0f50b61..7c1cae8f6 100644
--- a/src/video/win32_v.cpp
+++ b/src/video/win32_v.cpp
@@ -984,10 +984,10 @@ void VideoDriver_Win32Base::MainLoop()
 	}
 }
 
-void VideoDriver_Win32Base::ClientSizeChanged(int w, int h)
+void VideoDriver_Win32Base::ClientSizeChanged(int w, int h, bool force)
 {
 	/* Allocate backing store of the new size. */
-	if (this->AllocateBackingStore(w, h)) {
+	if (this->AllocateBackingStore(w, h, force)) {
 		/* Mark all palette colours dirty. */
 		_cur_palette.first_dirty = 0;
 		_cur_palette.count_dirty = 256;
@@ -1093,12 +1093,20 @@ bool VideoDriver_Win32Base::LockVideoBuffer()
 	if (this->draw_threaded) this->draw_lock.lock();
 
 	_screen.dst_ptr = this->GetVideoPointer();
+	assert(_screen.dst_ptr != nullptr);
 
 	return true;
 }
 
 void VideoDriver_Win32Base::UnlockVideoBuffer()
 {
+	assert(_screen.dst_ptr != nullptr);
+	if (_screen.dst_ptr != nullptr) {
+		/* Hand video buffer back to the drawing backend. */
+		this->ReleaseVideoPointer();
+		_screen.dst_ptr = nullptr;
+	}
+
 	if (this->draw_threaded) this->draw_lock.unlock();
 	this->buffer_locked = false;
 }
@@ -1239,9 +1247,16 @@ void VideoDriver_Win32GDI::Paint()
 				this->UpdatePalette(dc2, _local_palette.first_dirty, _local_palette.count_dirty);
 				break;
 
-			case Blitter::PALETTE_ANIMATION_BLITTER:
+			case Blitter::PALETTE_ANIMATION_BLITTER: {
+				bool need_buf = _screen.dst_ptr == nullptr;
+				if (need_buf) _screen.dst_ptr = this->GetVideoPointer();
 				blitter->PaletteAnimate(_local_palette);
+				if (need_buf) {
+					this->ReleaseVideoPointer();
+					_screen.dst_ptr = nullptr;
+				}
 				break;
+			}
 
 			case Blitter::PALETTE_ANIMATION_NONE:
 				break;
@@ -1336,7 +1351,7 @@ const char *VideoDriver_Win32OpenGL::Start(const StringList &param)
 		return err;
 	}
 
-	this->ClientSizeChanged(this->width, this->height);
+	this->ClientSizeChanged(this->width, this->height, true);
 
 	this->draw_threaded = false;
 	MarkWholeScreenDirty();
@@ -1403,17 +1418,18 @@ const char *VideoDriver_Win32OpenGL::AllocateContext()
 
 bool VideoDriver_Win32OpenGL::ToggleFullscreen(bool full_screen)
 {
+	if (_screen.dst_ptr != nullptr) this->ReleaseVideoPointer();
 	this->DestroyContext();
 	bool res = this->VideoDriver_Win32Base::ToggleFullscreen(full_screen);
 	res &= this->AllocateContext() == nullptr;
-	this->ClientSizeChanged(this->width, this->height);
+	this->ClientSizeChanged(this->width, this->height, true);
 	return res;
 }
 
 bool VideoDriver_Win32OpenGL::AfterBlitterChange()
 {
 	assert(BlitterFactory::GetCurrentBlitter()->GetScreenDepth() != 0);
-	this->ClientSizeChanged(this->width, this->height);
+	this->ClientSizeChanged(this->width, this->height, true);
 	return true;
 }
 
@@ -1426,8 +1442,13 @@ bool VideoDriver_Win32OpenGL::AllocateBackingStore(int w, int h, bool force)
 
 	if (this->gl_rc == nullptr) return false;
 
+	if (_screen.dst_ptr != nullptr) this->ReleaseVideoPointer();
+
 	this->dirty_rect = {};
-	return OpenGLBackend::Get()->Resize(w, h, force);
+	bool res = OpenGLBackend::Get()->Resize(w, h, force);
+	_screen.dst_ptr = this->GetVideoPointer();
+
+	return res;
 }
 
 void *VideoDriver_Win32OpenGL::GetVideoPointer()
@@ -1435,6 +1456,13 @@ void *VideoDriver_Win32OpenGL::GetVideoPointer()
 	return OpenGLBackend::Get()->GetVideoBuffer();
 }
 
+void VideoDriver_Win32OpenGL::ReleaseVideoPointer()
+{
+	OpenGLBackend::Get()->ReleaseVideoBuffer(this->dirty_rect);
+	this->dirty_rect = {};
+	_screen.dst_ptr = nullptr;
+}
+
 void VideoDriver_Win32OpenGL::Paint()
 {
 	PerformanceMeasurer framerate(PFE_VIDEO);
@@ -1459,10 +1487,8 @@ void VideoDriver_Win32OpenGL::Paint()
 		_cur_palette.count_dirty = 0;
 	}
 
-	OpenGLBackend::Get()->Paint(this->dirty_rect);
+	OpenGLBackend::Get()->Paint();
 	SwapBuffers(this->dc);
-
-	this->dirty_rect = {};
 }
 
 #endif /* WITH_OPENGL */
diff --git a/src/video/win32_v.h b/src/video/win32_v.h
index 85ac153bf..061f39c0a 100644
--- a/src/video/win32_v.h
+++ b/src/video/win32_v.h
@@ -63,7 +63,7 @@ protected:
 
 	void Initialize();
 	bool MakeWindow(bool full_screen);
-	void ClientSizeChanged(int w, int h);
+	void ClientSizeChanged(int w, int h, bool force = false);
 
 	/** Get screen depth to use for fullscreen mode. */
 	virtual uint8 GetFullscreenBpp();
@@ -71,6 +71,8 @@ protected:
 	virtual bool AllocateBackingStore(int w, int h, bool force = false) = 0;
 	/** Get a pointer to the video buffer. */
 	virtual void *GetVideoPointer() = 0;
+	/** Hand video buffer back to the painting backend. */
+	virtual void ReleaseVideoPointer() {}
 	/** Palette of the window has changed. */
 	virtual void PaletteChanged(HWND hWnd) = 0;
 
@@ -149,6 +151,7 @@ protected:
 
 	bool AllocateBackingStore(int w, int h, bool force = false) override;
 	void *GetVideoPointer() override;
+	void ReleaseVideoPointer() override;
 	void PaletteChanged(HWND hWnd) override {}
 
 	const char *AllocateContext();