3DSoftwareRenderer-DFSPR/Source/SDK/SpriteEngine/orthoAPI.h


#ifndef DFPSR_ORTHO
#define DFPSR_ORTHO

#include <assert.h>
#include "../../DFPSR/includeFramework.h"

namespace dsr {

// TODO: Give an ortho_ prefix
using Direction = int32_t;
static const Direction dir360 = 8;
static const Direction dir315 = 7;
static const Direction dir270 = 6;
static const Direction dir225 = 5;
static const Direction dir180 = 4;
static const Direction dir135 = 3;
static const Direction dir90 = 2;
static const Direction dir45 = 1;
static const Direction dir0 = 0;
inline int correctDirection(Direction direction) {
	return (int32_t)((uint32_t)((int32_t)direction + (dir360 * 1024)) % dir360);
}

// World 3D units
//   Tile = Diameter from one side to another along a standard tile
//     Used for expressing exact tile indices in games so that information can be stored efficiently
//   Mini-Tile = Tile / miniUnitsPerTile
//     Used to express locations in 3D without relying too much on non-deterministic floats
static constexpr int ortho_miniUnitsPerTile = 1024;
static constexpr float ortho_tilesPerMiniUnit = 1.0f / (float)ortho_miniUnitsPerTile;

int ortho_roundToTile(int miniCoordinate);
IVector3D ortho_roundToTile(const IVector3D& miniPosition);
float ortho_miniToFloatingTile(int miniCoordinate);
FVector3D ortho_miniToFloatingTile(const IVector3D& miniPosition);
int ortho_floatingTileToMini(float tileCoordinate);
IVector3D ortho_floatingTileToMini(const FVector3D& tilePosition);

// TODO: Make sure that every conversion is derived from a single pixel-rounded world-to-screen transform
//       Do this by letting it be the only argument for construction using integers
//       Everything else will simply be derived from it on construction
struct OrthoView {
public:
	// Unique integer for identifying the view
	int id = -1;

	// Direction for rotating sprites
	Direction worldDirection = dir0; // How are sprites in the world rotated relative to the camera's point of view

	// The rotating transform from normal-space to world-space.
	//   Light-space is a superset of normal-space with the origin around the camera. (Almost like camera-space but with Y straight up)
	FMatrix3x3 normalToWorldSpace;

	// Pixel aligned space (To ensure that moving one tile has the same number of pixels each time)
	IVector2D pixelOffsetPerTileX; // How many pixels does a sprite move per tile in X.
	IVector2D pixelOffsetPerTileZ; // How many pixels does a sprite move per tile in Z.
	int yPixelsPerTile = 0;

	// How pixels in the depth buffer maps to world-space coordinates in whole floating tiles.
	FMatrix3x3 screenDepthToWorldSpace;
	FMatrix3x3 worldSpaceToScreenDepth;
	// How pixels in the depth buffer maps to light-space coordinates in whole floating tiles.
	//   The origin is at the center of the image.
	//   The X and Y axis gives tile offsets in light space along the screen without depth information.
	//   The Z axis gives tile offset per mini-tile unit of height in the depth buffer.
	FMatrix3x3 screenDepthToLightSpace;
	FMatrix3x3 lightSpaceToScreenDepth;

	// Conversion systems between rounded pixels and XZ tiles along Y = 0
	FMatrix2x2 roundedScreenPixelsToWorldTiles; // TODO: Replace with a screenToTile sub-set
public:
	// TODO: Find a way to avoid the default constructor
	OrthoView() {}
	OrthoView(int id, const IVector2D roundedXAxis, const IVector2D roundedZAxis, int yPixelsPerTile, const FMatrix3x3 &normalToWorldSpace, Direction worldDirection)
	: id(id), worldDirection(worldDirection), normalToWorldSpace(normalToWorldSpace),
	  pixelOffsetPerTileX(roundedXAxis), pixelOffsetPerTileZ(roundedZAxis), yPixelsPerTile(yPixelsPerTile) {
		// Pixel aligned 3D transformation matrix from tile (x, y, z) to screen (x, y, h)
		FMatrix3x3 tileToScreen = FMatrix3x3(
			FVector3D(roundedXAxis.x, roundedXAxis.y, 0),
			FVector3D(0, -this->yPixelsPerTile, 1.0f),
			FVector3D(roundedZAxis.x, roundedZAxis.y, 0)
		);
		// Back from deep screen pixels to world tile coordinates
		FMatrix3x3 screenToTile = inverse(tileToScreen);

		// TODO: Obsolete
		this->roundedScreenPixelsToWorldTiles = inverse(FMatrix2x2(FVector2D(roundedXAxis.x, roundedXAxis.y), FVector2D(roundedZAxis.x, roundedZAxis.y)));

		// Save the conversion from screen-space to world-space in tile units
		this->screenDepthToWorldSpace = screenToTile;
		this->worldSpaceToScreenDepth = tileToScreen;

		// Save the conversion from screen-space to light-space in tile units
		this->screenDepthToLightSpace = FMatrix3x3(
		  this->normalToWorldSpace.transformTransposed(screenToTile.xAxis),
		  this->normalToWorldSpace.transformTransposed(screenToTile.yAxis),
		  this->normalToWorldSpace.transformTransposed(screenToTile.zAxis)
		);
		this->lightSpaceToScreenDepth = inverse(this->screenDepthToLightSpace);
	}
public:
	IVector2D miniTileOffsetToScreenPixel(const IVector3D& miniTileOffset) const {
		IVector2D centeredPixelLocation = this->pixelOffsetPerTileX * miniTileOffset.x + this->pixelOffsetPerTileZ * miniTileOffset.z;
		centeredPixelLocation.y -= miniTileOffset.y * this->yPixelsPerTile;
		return centeredPixelLocation / ortho_miniUnitsPerTile;
	}
	// Position is expressed in world space using mini units
	IVector2D miniTilePositionToScreenPixel(const IVector3D& position, const IVector2D& worldCenter) const {
		return this->miniTileOffsetToScreenPixel(position) + worldCenter;
	}
	// Returns the 3D mini-tile units moved along the ground for the pixel offset
	//   Only rotation and scaling for pixel offsets
	FVector3D pixelToTileOffset(const IVector2D& pixelOffset) const {
		FVector2D xzTiles = this->roundedScreenPixelsToWorldTiles.transform(FVector2D(pixelOffset.x, pixelOffset.y));
		return FVector3D(xzTiles.x, 0.0f, xzTiles.y);
	}
	IVector3D pixelToMiniOffset(const IVector2D& pixelOffset) const {
		FVector3D tiles = this->pixelToTileOffset(pixelOffset);
		return IVector3D(ortho_floatingTileToMini(tiles.x), 0, ortho_floatingTileToMini(tiles.z));
	}
	// Returns the 3D mini-tile location for a certain pixel on the screen intersecting with the ground
	//   Full transform for pixel locations
	IVector3D pixelToMiniPosition(const IVector2D& pixelLocation, const IVector2D& worldCenter) const {
		return this->pixelToMiniOffset(pixelLocation - worldCenter);
	}
};

// How to use the orthogonal system
//   * Place tiles in whole tile integer units
//     Multiply directly with pixelOffsetPerTileX and pixelOffsetPerTileZ to get deterministic pixel offsets
//   * Define sprites in mini units (1 tile = ortho_miniUnitsPerTile mini units)
//     First multiply mini units with yPixelsPerTile, pixelOffsetPerTileX and pixelOffsetPerTileZ for each 3D coordinate
//     Then divide by ortho_miniUnitsPerTile, which most processors should have custom instructions for handling quickly
//     With enough bits in the integers, the result should be steady and not shake around randomly
struct OrthoSystem {
public:
	static constexpr int maxCameraAngles = 8;
	static constexpr float diag = 0.707106781f; // cos(45 degrees) = Sqrt(2) / 2
	// Persistent settings
	float cameraTilt; // Camera coefficient. (-inf is straight down, -1 is diagonal down, 0 is horizontal)
	int pixelsPerTile; // The sideway length of a tile in pixels when seen from straight ahead.
	// Generated views
	OrthoView view[maxCameraAngles];
private:
	// Update generated settings from persistent settings
	// Enforces a valid orthogonal camera system
	void update() {
		// Calculate y offset rounded to whole tiles to prevent random gaps in grids
		int yPixelsPerTile = (float)this->pixelsPerTile / sqrt(this->cameraTilt * this->cameraTilt + 1);

		// Define sprite directions
		FVector3D upAxis = FVector3D(0.0f, 1.0f, 0.0f);
		Direction worldDirections[8] = {dir315, dir45, dir135, dir225, dir0, dir90, dir180, dir270};
		// Define approximate camera systems just to get something axis aligned
		FMatrix3x3 cameraSystems[8];
		cameraSystems[0] = FMatrix3x3::makeAxisSystem(FVector3D(diag, this->cameraTilt, diag), upAxis);
		cameraSystems[1] = FMatrix3x3::makeAxisSystem(FVector3D(-diag, this->cameraTilt, diag), upAxis);
		cameraSystems[2] = FMatrix3x3::makeAxisSystem(FVector3D(-diag, this->cameraTilt, -diag), upAxis);
		cameraSystems[3] = FMatrix3x3::makeAxisSystem(FVector3D(diag, this->cameraTilt, -diag), upAxis);
		cameraSystems[4] = FMatrix3x3::makeAxisSystem(FVector3D( 0, this->cameraTilt, 1), upAxis);
		cameraSystems[5] = FMatrix3x3::makeAxisSystem(FVector3D(-1, this->cameraTilt, 0), upAxis);
		cameraSystems[6] = FMatrix3x3::makeAxisSystem(FVector3D( 0, this->cameraTilt,-1), upAxis);
		cameraSystems[7] = FMatrix3x3::makeAxisSystem(FVector3D( 1, this->cameraTilt, 0), upAxis);

		for (int a = 0; a < maxCameraAngles; a++) {
			// Define the coordinate system for normals
			FVector3D normalSystemDirection = cameraSystems[a].zAxis;
			normalSystemDirection.y = 0.0f;
			FMatrix3x3 normalToWorldSpace = FMatrix3x3::makeAxisSystem(normalSystemDirection, FVector3D(0.0f, 1.0f, 0.0f));
			// Create an axis system truncated inwards to whole pixels to prevent creating empty seams between tile aligned sprites
			Camera approximateCamera = Camera::createOrthogonal(Transform3D(FVector3D(), cameraSystems[a]), this->pixelsPerTile, this->pixelsPerTile, 0.5f);
			float halfTile = (float)this->pixelsPerTile * 0.5f;
			FVector2D XAxis = approximateCamera.worldToScreen(FVector3D(1.0f, 0.0f, 0.0f)).is - halfTile;
			FVector2D ZAxis = approximateCamera.worldToScreen(FVector3D(0.0f, 0.0f, 1.0f)).is - halfTile;
			this->view[a] = OrthoView(
			  a,
			  IVector2D((int)XAxis.x, (int)XAxis.y),
			  IVector2D((int)ZAxis.x, (int)ZAxis.y),
			  yPixelsPerTile,
			  normalToWorldSpace,
			  worldDirections[a]
			);
		}
	}
public:
	OrthoSystem() : cameraTilt(0), pixelsPerTile(0) {}
	OrthoSystem(float cameraTilt, int pixelsPerTile) : cameraTilt(cameraTilt), pixelsPerTile(pixelsPerTile) {
		this->update();
	}
	explicit OrthoSystem(const ReadableString& content) {
		config_parse_ini(content, [this](const ReadableString& block, const ReadableString& key, const ReadableString& value) {
			if (string_length(block) == 0) {
				if (string_caseInsensitiveMatch(key, U"DownTiltPerThousand")) {
					this->cameraTilt = (float)string_toInteger(value) * -0.001f;
				} else if (string_caseInsensitiveMatch(key, U"PixelsPerTile")) {
					this->pixelsPerTile = string_toInteger(value);
				} else {
					printText("Unrecognized key \"", key, "\" in orthogonal camera configuration file.\n");
				}
			} else {
				printText("Unrecognized block \"", block, "\" in orthogonal camera configuration file.\n");
			}
		});
		this->update();
	}
public:
	IVector2D miniTileOffsetToScreenPixel(const IVector3D& miniTileOffset, int cameraIndex) const {
		return this->view[cameraIndex].miniTileOffsetToScreenPixel(miniTileOffset);
	}
	// Position is expressed in world space using mini units
	IVector2D miniTilePositionToScreenPixel(const IVector3D& position, int cameraIndex, const IVector2D& worldCenter) const {
		return this->view[cameraIndex].miniTilePositionToScreenPixel(position, worldCenter);
	}
public:
	// Returns the 3D mini-tile units moved along the ground for the pixel offset
	//   Only rotation and scaling for pixel offsets
	FVector3D pixelToTileOffset(const IVector2D& pixelOffset, int cameraIndex) const {
		return this->view[cameraIndex].pixelToTileOffset(pixelOffset);
	}
	IVector3D pixelToMiniOffset(const IVector2D& pixelOffset, int cameraIndex) const {
		return this->view[cameraIndex].pixelToMiniOffset(pixelOffset);
	}
	// Returns the 3D mini-tile location for a certain pixel on the screen intersecting with the ground
	//   Full transform for pixel locations
	IVector3D pixelToMiniPosition(const IVector2D& pixelLocation, int cameraIndex, const IVector2D& worldCenter) const {
		return this->view[cameraIndex].pixelToMiniPosition(pixelLocation, worldCenter);
	}
};

}

#endif