Add: [OpenGL] Support for a separate animation buffer that stores the palette values of the screen in addition to the colour buffer.

src/blitter/base.hpp

@@ -185,6 +185,14 @@ public:
 	 */
 	virtual Blitter::PaletteAnimation UsePaletteAnimation() = 0;
 
+	/**
+	 * Does this blitter require a separate animation buffer from the video backend?
+	 */
+	virtual bool NeedsAnimationBuffer()
+	{
+		return false;
+	}
+
 	/**
 	 * Get the name of the blitter, the same as the Factory-instance returns.
 	 */

src/video/opengl.cpp

@@ -392,8 +392,10 @@ OpenGLBackend::~OpenGLBackend()
 	if (_glDeleteBuffers != nullptr) {
 		_glDeleteBuffers(1, &this->vbo_quad);
 		_glDeleteBuffers(1, &this->vid_pbo);
+		_glDeleteBuffers(1, &this->anim_pbo);
 	}
 	glDeleteTextures(1, &this->vid_texture);
+	glDeleteTextures(1, &this->anim_texture);
 	glDeleteTextures(1, &this->pal_texture);
 }
 
@@ -458,6 +460,17 @@ const char *OpenGLBackend::Init()
 	glBindTexture(GL_TEXTURE_2D, 0);
 	if (glGetError() != GL_NO_ERROR) return "Can't generate video buffer texture";
 
+	/* Setup video buffer texture. */
+	glGenTextures(1, &this->anim_texture);
+	glBindTexture(GL_TEXTURE_2D, this->anim_texture);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 0);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+	glBindTexture(GL_TEXTURE_2D, 0);
+	if (glGetError() != GL_NO_ERROR) return "Can't generate animation buffer texture";
+
 	/* Setup palette texture. */
 	glGenTextures(1, &this->pal_texture);
 	glBindTexture(GL_TEXTURE_1D, this->pal_texture);
@@ -505,10 +518,13 @@ const char *OpenGLBackend::Init()
 	_glUniform1i(tex_location, 0);     // Texture unit 0.
 	_glUniform1i(palette_location, 1); // Texture unit 1.
 	_glUniform1i(remap_location, 2);   // Texture unit 2.
+	(void)glGetError(); // Clear errors.
 
 	/* Create pixel buffer object as video buffer storage. */
 	_glGenBuffers(1, &this->vid_pbo);
 	_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, this->vid_pbo);
+	_glGenBuffers(1, &this->anim_pbo);
+	_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, this->anim_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
@@ -686,7 +702,7 @@ bool OpenGLBackend::Resize(int w, int h, bool force)
 	if (!force && _screen.width == w && _screen.height == h) return false;
 
 	int bpp = BlitterFactory::GetCurrentBlitter()->GetScreenDepth();
-	int pitch = bpp != 32 ? Align(w, 4) : w;
+	int pitch = Align(w, 4);
 
 	glViewport(0, 0, w, h);
 
@@ -715,6 +731,23 @@ bool OpenGLBackend::Resize(int w, int h, bool force)
 			glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, w, h, 0, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV, nullptr);
 			break;
 	}
+
+	/* Does this blitter need a separate animation buffer? */
+	if (BlitterFactory::GetCurrentBlitter()->NeedsAnimationBuffer()) {
+		_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, this->anim_pbo);
+		_glBufferData(GL_PIXEL_UNPACK_BUFFER, pitch * h, NULL, 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->anim_texture);
+		glTexImage2D(GL_TEXTURE_2D, 0, GL_R8, w, h, 0, GL_RED, GL_UNSIGNED_BYTE, NULL);
+	} else {
+		/* Allocate dummy texture that always reads as 0 == no remap. */
+		uint dummy = 0;
+		glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
+		glBindTexture(GL_TEXTURE_2D, this->anim_texture);
+		glTexImage2D(GL_TEXTURE_2D, 0, GL_R8, 1, 1, 0, GL_RED, GL_UNSIGNED_BYTE, &dummy);
+	}
+
 	glBindTexture(GL_TEXTURE_2D, 0);
 
 	/* Set new viewport. */
@@ -761,7 +794,18 @@ void OpenGLBackend::Paint()
 	glBindTexture(GL_TEXTURE_2D, this->vid_texture);
 	_glActiveTexture(GL_TEXTURE1);
 	glBindTexture(GL_TEXTURE_1D, this->pal_texture);
-	_glUseProgram(BlitterFactory::GetCurrentBlitter()->GetScreenDepth() == 8 ? this->pal_program : this->vid_program);
+	/* Is the blitter relying on a separate animation buffer? */
+	if (BlitterFactory::GetCurrentBlitter()->NeedsAnimationBuffer()) {
+		_glActiveTexture(GL_TEXTURE2);
+		glBindTexture(GL_TEXTURE_2D, this->anim_texture);
+		_glUseProgram(this->remap_program);
+		_glUniform4f(this->remap_sprite_loc, 0.0f, 0.0f, 1.0f, 1.0f);
+		_glUniform2f(this->remap_screen_loc, 1.0f, 1.0f);
+		_glUniform1f(this->remap_zoom_loc, 0);
+		_glUniform1i(this->remap_rgb_loc, 1);
+	} else {
+		_glUseProgram(BlitterFactory::GetCurrentBlitter()->GetScreenDepth() == 8 ? this->pal_program : this->vid_program);
+	}
 	_glBindVertexArray(this->vao_quad);
 	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 
@@ -814,6 +858,18 @@ void *OpenGLBackend::GetVideoBuffer()
 	return _glMapBuffer(GL_PIXEL_UNPACK_BUFFER, GL_READ_WRITE);
 }
 
+/**
+ * Get a pointer to the memory for the separate animation buffer.
+ * @return Pointer to draw on.
+ */
+uint8 *OpenGLBackend::GetAnimBuffer()
+{
+	if (this->anim_pbo == 0) return nullptr;
+
+	_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, this->anim_pbo);
+	return (uint8 *)_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.
@@ -842,6 +898,26 @@ void OpenGLBackend::ReleaseVideoBuffer(const Rect &update_rect)
 	}
 }
 
+/**
+ * Update animation buffer texture after the animation buffer was filled.
+ * @param update_rect Rectangle encompassing the dirty region of the animation buffer.
+ */
+void OpenGLBackend::ReleaseAnimBuffer(const Rect &update_rect)
+{
+	if (this->anim_pbo == 0) return;
+
+	_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, this->anim_pbo);
+	_glUnmapBuffer(GL_PIXEL_UNPACK_BUFFER);
+
+	/* Update changed rect of the video buffer texture. */
+	if (update_rect.left != update_rect.right) {
+		_glActiveTexture(GL_TEXTURE0);
+		glBindTexture(GL_TEXTURE_2D, this->anim_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_RED, GL_UNSIGNED_BYTE, (GLvoid *)(size_t)(update_rect.top * _screen.pitch + update_rect.left));
+	}
+}
+
 /* virtual */ Sprite *OpenGLBackend::Encode(const SpriteLoader::Sprite *sprite, AllocatorProc *allocator)
 {
 	/* Allocate and construct sprite data. */

src/video/opengl.h

@@ -39,6 +39,9 @@ private:
 	GLuint vbo_quad;    ///< Vertex buffer with a fullscreen quad.
 	GLuint pal_texture; ///< Palette lookup texture.
 
+	GLuint anim_pbo;     ///< Pixel buffer object storing the memory used for the animation buffer.
+	GLuint anim_texture; ///< Texture handle for the animation buffer texture.
+
 	GLuint remap_program;    ///< Shader program for blending and rendering a RGBA + remap texture.
 	GLint  remap_sprite_loc; ///< Uniform location for sprite parameters.
 	GLint  remap_screen_loc; ///< Uniform location for screen size;
@@ -72,7 +75,9 @@ public:
 	void ClearCursorCache();
 
 	void *GetVideoBuffer();
+	uint8 *GetAnimBuffer();
 	void ReleaseVideoBuffer(const Rect &update_rect);
+	void ReleaseAnimBuffer(const Rect &update_rect);
 
 	/* SpriteEncoder */
 

src/video/video_driver.hpp

@@ -121,6 +121,24 @@ public:
 		return false;
 	}
 
+	/**
+	 * Does this video driver support a separate animation buffer in addition to the colour buffer?
+	 * @return True if a separate animation buffer is supported.
+	 */
+	virtual bool HasAnimBuffer()
+	{
+		return false;
+	}
+
+	/**
+	 * Get a pointer to the animation buffer of the video back-end.
+	 * @return Pointer to the buffer or nullptr if no animation buffer is supported.
+	 */
+	virtual uint8 *GetAnimBuffer()
+	{
+		return nullptr;
+	}
+
 	/**
 	 * An edit box lost the input focus. Abort character compositing if necessary.
 	 */

src/video/win32_v.cpp

@@ -1545,14 +1545,19 @@ bool VideoDriver_Win32OpenGL::AllocateBackingStore(int w, int h, bool force)
 
 void *VideoDriver_Win32OpenGL::GetVideoPointer()
 {
+	if (BlitterFactory::GetCurrentBlitter()->NeedsAnimationBuffer()) {
+		this->anim_buffer = OpenGLBackend::Get()->GetAnimBuffer();
+	}
 	return OpenGLBackend::Get()->GetVideoBuffer();
 }
 
 void VideoDriver_Win32OpenGL::ReleaseVideoPointer()
 {
+	if (this->anim_buffer != nullptr) OpenGLBackend::Get()->ReleaseAnimBuffer(this->dirty_rect);
 	OpenGLBackend::Get()->ReleaseVideoBuffer(this->dirty_rect);
 	this->dirty_rect = {};
 	_screen.dst_ptr = nullptr;
+	this->anim_buffer = nullptr;
 }
 
 void VideoDriver_Win32OpenGL::Paint()

src/video/win32_v.h

@@ -128,7 +128,7 @@ public:
 /** The OpenGL video driver for windows. */
 class VideoDriver_Win32OpenGL : public VideoDriver_Win32Base {
 public:
-	VideoDriver_Win32OpenGL() : dc(nullptr), gl_rc(nullptr) {}
+	VideoDriver_Win32OpenGL() : dc(nullptr), gl_rc(nullptr), anim_buffer(nullptr) {}
 
 	const char *Start(const StringList &param) override;
 
@@ -144,12 +144,16 @@ public:
 
 	void ClearSystemSprites() override;
 
+	bool HasAnimBuffer() override { return true; }
+	uint8 *GetAnimBuffer() override { return this->anim_buffer; }
+
 	const char *GetName() const override { return "win32-opengl"; }
 
 protected:
-	HDC   dc;          ///< Window device context.
-	HGLRC gl_rc;       ///< OpenGL context.
-	bool  vsync;       ///< Enable VSync?
+	HDC    dc;          ///< Window device context.
+	HGLRC  gl_rc;       ///< OpenGL context.
+	bool   vsync;       ///< Enable VSync?
+	uint8 *anim_buffer; ///< Animation buffer from OpenGL back-end.
 
 	uint8 GetFullscreenBpp() override { return 32; } // OpenGL is always 32 bpp.