/*
 * DSFML - The Simple and Fast Multimedia Library for D
 *
 * Copyright (c) 2013 - 2018 Jeremy DeHaan (dehaan.jeremiah@gmail.com)
 *
 * This software is provided 'as-is', without any express or implied warranty.
 * In no event will the authors be held liable for any damages arising from the
 * use of this software.
 *
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 *
 * 1. The origin of this software must not be misrepresented; you must not claim
 * that you wrote the original software. If you use this software in a product,
 * an acknowledgment in the product documentation would be appreciated but is
 * not required.
 *
 * 2. Altered source versions must be plainly marked as such, and must not be
 * misrepresented as being the original software.
 *
 * 3. This notice may not be removed or altered from any source distribution
 *
 *
 * DSFML is based on SFML (Copyright Laurent Gomila)
 */

/**
 * $(U RenderTarget) defines the common behaviour of all the 2D render targets
 * usable in the graphics module. It makes it possible to draw 2D entities like
 * sprites, shapes, text without using any OpenGL command directly.
 *
 * A $(U RenderTarget) is also able to use views which are a kind of 2D cameras.
 * With views you can globally scroll, rotate or zoom everything that is drawn,
 * without having to transform every single entity.
 *
 * On top of that, render targets are still able to render direct OpenGL stuff.
 * It is even possible to mix together OpenGL calls and regular DSFML drawing
 * commands. When doing so, make sure that OpenGL states are not messed up by
 * calling the `pushGLStates`/`popGLStates` functions.
 *
 * See_Also:
 * $(RENDERWINDOW_LINK), $(RENDERTEXTURE_LINK), $(VIEW_LINK)
 */
module nudsfml.graphics.rendertarget;

import bindbc.sfml.graphics;

import nudsfml.graphics.renderwindow;
import nudsfml.graphics.rendertexture;
import nudsfml.graphics.drawable;
import nudsfml.graphics.renderstates;

import nudsfml.graphics.primitivetype;
import nudsfml.graphics.vertex;
import nudsfml.graphics.view;
import nudsfml.graphics.color;
import nudsfml.graphics.rect;

import nudsfml.system.vector2;

/**
 * Base interface for all render targets (window, texture, ...).
 */
interface RenderTarget
{
	@property
	{
		/**
	 	 * The current active view.
	 	 *
	 	 * The view is like a 2D camera, it controls which part of the 2D scene
		 * is visible, and how it is viewed in the render-target. The new view
		 * will affect everything that is drawn, until another view is set.
	 	 *
	 	 * The render target keeps its own copy of the view object, so it is not
	 	 * necessary to keep the original one alive after calling this function.
		 * To restore the original view of the target, you can pass the result
		 * of `getDefaultView()` to this function.
	 	 */
		View view(View newView);

		/// ditto
		View view() const;
	}

	/**
	 * Get the default view of the render target.
	 *
	 * The default view has the initial size of the render target, and never
	 * changes after the target has been created.
	 *
	 * Returns: The default view of the render target.
	 */
	View getDefaultView() const;

	/**
	 * Return the size of the rendering region of the target.
	 *
	 * Returns: Size in pixels.
	 */
	Vector2u getSize() const;

	/**
	 * Get the viewport of a view, applied to this render target.
	 *
	 * The viewport is defined in the view as a ratio, this function simply
	 * applies this ratio to the current dimensions of the render target to
	 * calculate the pixels rectangle that the viewport actually covers in the
	 * target.
	 *
	 * Params:
	 * 		view	= The view for which we want to compute the viewport
	 *
	 * Returns: Viewport rectangle, expressed in pixels.
	 */
	final IntRect getViewport(View view) const
	{
		float width = getSize().x;
		float height = getSize().y;

		return IntRect(cast(int)(0.5 + width * view.viewport.left),
						cast(int)(0.5 + height * view.viewport.top),
						cast(int)(0.5 + width * view.viewport.width),
						cast(int)(0.5 + height * view.viewport.height));
	}

	/**
	 * Clear the entire target with a single color.
	 *
	 * This function is usually called once every frame, to clear the previous
	 * contents of the target.
	 *
	 * Params:
	 * 		color	= Fill color to use to clear the render target
	 */
	void clear(Color color = Color.Black);

	/**
	 * Draw a drawable object to the render target.
	 *
	 * Params:
	 * 		drawable	= Object to draw
	 * 		states		= Render states to use for drawing
	 */
	void draw(Drawable drawable, RenderStates states = RenderStates.init);

	/**
	 * Draw primitives defined by an array of vertices.
	 *
	 * Params:
	 * 		vertices	= Array of vertices to draw
	 * 		type		= Type of primitives to draw
	 * 		states		= Render states to use for drawing
	 */
	void draw(const(Vertex)[] vertices, PrimitiveType type, RenderStates states = RenderStates.init);

	/**
	 * Convert a point fom target coordinates to world coordinates, using the
	 * current view.
	 *
	 * This function is an overload of the mapPixelToCoords function that
	 * implicitely uses the current view.
	 *
	 * Params:
	 * 		point	= Pixel to convert
	 *
	 * Returns: The converted point, in "world" coordinates.
	 */
	final Vector2f mapPixelToCoords(Vector2i point) inout
	{
		return mapPixelToCoords(point, view);
	}

	/**
	 * Convert a point from target coordinates to world coordinates.
	 *
	 * This function finds the 2D position that matches the given pixel of the
	 * render-target. In other words, it does the inverse of what the graphics
	 * card does, to find the initial position of a rendered pixel.
	 *
	 * Initially, both coordinate systems (world units and target pixels) match
	 * perfectly. But if you define a custom view or resize your render-target,
	 * this assertion is not true anymore, ie. a point located at (10, 50) in
	 * your render-target may map to the point (150, 75) in your 2D world – if
	 * the view is translated by (140, 25).
	 *
	 * For render-windows, this function is typically used to find which point
	 * (or object) is located below the mouse cursor.
	 *
	 * This version uses a custom view for calculations, see the other overload
	 * of the function if you want to use the current view of the render-target.
	 *
	 * Params:
	 * 		point	= Pixel to convert
	 * 		theView	= The view to use for converting the point
	 *
	 * Returns: The converted point, in "world" coordinates.
	 */
	final Vector2f mapPixelToCoords(Vector2i point, View theView) inout
	{
	    // First, convert from viewport coordinates to homogeneous coordinates
		Vector2f normalized;

		normalized.x = -1.0 + 2.0 * (cast(float)point.x - theView.viewport.left) / theView.viewport.width;
		normalized.y = -1.0 + 2.0 * (cast(float)point.y - theView.viewport.top) / theView.viewport.height;

	    // Then transform by the inverse of the view matrix
		return view.getInverseTransform().transformPoint(normalized);
	}

	/**
	 * Convert a point from target coordinates to world coordinates, using the
	 * curtheView.view.
	 *
	 * This function is an overload of the mapPixelToCoords function that
	 * implicitely uses the current view.
	 *
	 * Params:
	 * 		point	= Point to convert
	 *
	 * Returns: The converted point, in "world" coordinates.
	 */
	final Vector2i mapCoordsToPixel(Vector2f point) inout
	{
		return mapCoordsToPixel(point, view);
	}

	/**
	 * Convert a point from world coordinates to target coordinates.
	 *
	 * This function finds the pixel of the render-target that matches the given
	 * 2D point. In other words, it goes through the same process as the
	 * graphics card, to compute the final position of a rendered point.
	 *
	 * Initially, both coordinate systems (world units and target pixels) match
	 * perfectly. But if you define a custom view or resize your render-target,
	 * this assertion is not true anymore, ie. a point located at (150, 75) in
	 * your 2D world may map to the pixel (10, 50) of your render-target – if
	 * the view is translated by (140, 25).
	 *
	 * This version uses a custom view for calculations, see the other overload
	 * of the function if you want to use the current view of the render-target.
	 *
	 * Params:
	 * 		point	= Point to convert
	 * 		theView	= The view to use for converting the point
	 *
	 * Returns: The converted point, in target coordinates (pixels).
	 */
	final Vector2i mapCoordsToPixel(Vector2f point, View theView) inout
	{
		// First, transform the point by the view matrix
		Vector2f normalized = theView.getTransform().transformPoint(point);

		// Then convert to viewport coordinates
		Vector2i pixel;
		pixel.x = cast(int)(( normalized.x + 1.0) / 2.0 * theView.viewport.width  + theView.viewport.left);
		pixel.y = cast(int)((-normalized.y + 1.0) / 2.0 * theView.viewport.height + theView.viewport.top);

		return pixel;
	}

	/**
	 * Restore the previously saved OpenGL render states and matrices.
	 *
	 * See the description of `pushGLStates` to get a detailed description of
	 * these functions.
	 */
	void popGLStates();

	/**
     * Save the current OpenGL render states and matrices.
     *
     * This function can be used when you mix SFML drawing and direct OpenGL
     * rendering. Combined with PopGLStates, it ensures that:
     * $(UL
     * $(LI DSFML's internal states are not messed up by your OpenGL code)
     * $(LI your OpenGL states are not modified by a call to an SFML function))
     *
     * $(PARA More specifically, it must be used around the code that calls
     * `draw` functions.
     *
     * Note that this function is quite expensive: it saves all the possible
	 * OpenGL states and matrices, even the ones you don't care about.Therefore
	 * it should be used wisely. It is provided for convenience, but the best
	 * results will be achieved if you handle OpenGL states yourself (because
	 * you know which states have really changed, and need to be saved and
	 * restored). Take a look at the `resetGLStates` function if you do so.)
     */
	void pushGLStates();

	/**
	 * Reset the internal OpenGL states so that the target is ready for drawing.
	 *
	 * This function can be used when you mix SFML drawing and direct OpenGL
	 * rendering, if you choose not to use `pushGLStates`/`popGLStates`. It
	 * makes sure that all OpenGL states needed by SFML are set, so that
	 * subsequent `draw()` calls will work as expected.
	 */
	void resetGLStates();
}