MonoGame Pixel Planets
======================
Originally created by Deep-Fold, ported by Enthusiast Guy


0. Showcase
============

https://www.youtube.com/watch?v=wnwpnkBD6OQ


1. About
=========

1.1. This document history
----------------------------
13.03.2021
- added this history section for updates that people who read this long text before can jump straight to without re-reading;
- updated sections: 2.1.2. Shaders; 

1.2. Personal note
------------------

This project is somewhat branched off this one right here: https://github.com/Deep-Fold/PixelPlanets
The author, Deep-Fold is the original wizard of all this, and large amounts of hails should go his way.
Please visit his itch.io project page here: https://deep-fold.itch.io/pixel-planet-generator

I'm the Enthusiast Guy, responsible for this port to Monogame. You can find me on YouTube:
https://www.youtube.com/channel/UCs3I6aDQ6Hj7m6_9l0HBgQA

I've stumbled upon this crazy cool gem just a few days before writing this. I have my own game project that
I'm working on, and it so happened that I needed planets for some parts of my game. The original project is
written with Godot (https://godotengine.org), however my own game project is written quite extensively in
MonoGame. The shaders Deep-Fold wrote are in GLSL language (https://en.wikipedia.org/wiki/OpenGL_Shading_Language)
while monogame uses HLSL (https://en.wikipedia.org/wiki/High-Level_Shading_Language). Basically think of them
as OpenGL vs DirectX. Because Monogame's ancestor is XNA written by Microsoft for XBox360, you can see why it
would not use OpenGL shaders.

I have never worked with shaders before this, but I had hoped that this wonderful project can somehow be
converted to the HLSL that monogame supports, and in fact, it did as this very project stands whitness for.

Following Deep-Fold's nice guidance in this new chapter of shaders, I was able to port this, while
honestly not fully understanding the whole math behind it. For the moment, at least.


1.3. Further development/support
--------------------------------

I do intend to bring this one to a stable form, as accurate as possible and I'll provide moderate support if
any bugs are reported, however, please consider that my main work is concentrated elsewhere and I may not have
time for substantial features. Moreover, I believe this should remain a rather simple project.
Feel free to fork it, though, and let me know what you did with it. ;)

1.4. Use/LICENSE
----------------

The original author released his work under MIT license and specifically mentioned we can do anything we
want with it, under any circumstances, while, (not obligatory) a mention of his name would be nice.
The same conditions are valid here. So:

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
associated documentation files (the "Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the
following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial
portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.





2. Project
===========

Important.
This project is NOT an example in code tidyness. Please don't assume it is. I took a lot of shortcuts to get
to the desired result, as the central piece of this is the actual shaders, not the code architecture.

2.1. Structure
--------------

2.1.1. Entry point
------------------
The entry point of the application is the PixelPlanets.cs class. It contains the most important methods:

Update() and Draw().

Ideally Update should prepare everything in a state and Draw just to simply draw. I probably not respected that
thoroughly, but make sure you do if you use MonoGame to build your game.

The State.cs class contains the state of most things in this app. It also contains the persisted data that is
saveable to state.json with F1.

2.1.2. Shaders
--------------
As of version 1.2.0.17, the whole project has been migrated from MonoGame 3.7 to 3.8. This somehow introduced a problem
in the shaders manifesting when attempting to compile the shaders: "unable to unroll loop, loop does not appear to terminate in a timely manner"
After a bit of investigation it seems that the solution was to change one single line in planet_utils.fx:
from
	#define PS_SHADERMODEL ps_4_0_level_9_1
to
	#define PS_SHADERMODEL ps_4_0

as per the documentation available here: https://docs.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-models?redirectedfrom=MSDN
(see the shader profiles there)
it seems that initially I was using Shader model 2. Now, by simply changing that line, the shader model has been changed to 4.0, thus
removing the initial issue. Clearly, devices that don't support shader model 4 can no longer run this code. Attempting to change to 3.0
was met with: "Pixel shader must be SM 4.0 level 9.1 or higher".

You'll find the shaders in the Content/ShadersV2 directory. All the shaders drawing planets/stars use
a common shader included in all of them at the beginning, called "planet_utils.fx". That holds the
common math used all over.
Each shader has some "parameters" which means it accepts variables from the calling program and uses
them further. Those params are not static, they look something like:

float time = 0.0;

This indicates that MonoGame is able to send values to them like this:

shader.Parameters["time"].SetValue(yourFloatValueHere); // See Shaders.cs for that

Many shaders consist of some layer methods that are used in the MainPS method.
MainPS receives a VertexShaderInput input parameter that holds the TextureCoordinates that mean the actual XY of the current pixel
Then, other layer methods are called with those coordinates to render gradually the land, lakes and clouds, whatever may be the
case, and then they are returned from the MainPS once again as the final color for the respective XY pixel.

2.1.3. Debugging shaders
------------------------

Arm yourself with patience.
To compile a shader, you need to run Content.mgcb from your project/Content folder. That, should ideally launch the MonoGame
Pipeline Tool. If, instead of that, you open a text file, then right click on Content.mgcb, select Open With and in the
window that opens, find "MonoGame Pipeline Tool". Select it, click on Make Default and then OK.

Right click on a shader in ShadersV2 and select Rebuild. That will rebuild only the selected shader. If the build output
shows the build with green, it means it compiled correctly all code in there. If not, then you need to debug.

First annoying thing (and it's partly my fault) is that because I introduced the #include, the line numbers no longer correspond
as they should when they show you an error. They show a number higher then where the actual problem is. That is really
annoying, but a workaround is to copy ALL methods from the "planet_utils.fx" in your working shader and get rid of the #include
temporarily. Once you fix the problem(s) you can restore the structure.

While it may be inconvenient to do this, please resist writing permanent duplicate code. Trust me, in the long term it will backfire.

Keep in mind that shaders are pre-optimized by the engine. This means that if you comment a piece of code, the engine will aggressively
go up the execution line and obliderate anything connected to the code you commented, considering that code should no longer exist.
This includes parameters, so you CAN get an error when trying to pass a parameter not used, because it is NO LONGER exposed.

While in GLSL you may declare a vec2 like this: vec2(.5), which means actually vec2(.5, .5), you can't get away with this in HLSL.
You need to explicitly declare float2(.5, .5), otherwise you'll get an error.

2.1.4. Packages
---------------

This project uses Newtonsoft json to serialize/deserialize the state data.


3. Version history
==================

1.2.0.17 - march 13'th 2021

- Migrated from MonoGame 3.7 to 3.8.0.1641;
- Small refactoring.




0.2.0.17 - march 3'rd 2021 - The very first published version. It is an alpha version, meaning not all features are yet
connected, and some are downright missing (for now).

Features:
------------
- GLSL to HLSL conversion of ALL pixel shaders available in the original Pixel Planets project:
(Asteroid, GasPlanet, IceWorld, LandMasses, LandRivers, LavaWorld, NoAtmosphere, Star, TerranDry)
- Some optimizations or refactoring of the shaders as permitted by the MonoGame architecture;
- Canvas representation of the planets;

Userinterface
- Browse through the planets (use keys LEFT/RIGHT to show previous/next planet);
- Randomize the parameters for the shader. This can get quite messy, still experimental. Procedural generation
is far better, but this will be implemented later.
- Set all parameters back to default by using the TILDE key (it's usually above TAB);
- Increase/decrease planet resolution (use keys UP/DOWN);
- Stop the planet from rotating (use key SPACE);
- Move the light source around (use mouse left click and move around);
- Manually rotate planet with the mouse (use mouse right click and move around);
- List of modifiable parameters for all shaders;
- Left click on any parameter, hold and scroll mouse wheel to change the value. The change is instantly observed
in the viewport;
- While editing a parameter, you can press middle mouse button to revert that value to the default;
- State save (use F1 to save current state to an editable state.json in the app directory). As long as the state.json
exists in the root of the project, it will be loaded on start-up. Deleting it will force the application to generate
a new set. Be careful when you edit it, I made no guards over bad edits and the application will most certainly crash;
The state holds parameter values for all planets, assuming I've finished adding them;
- Esc key exits the app;

Known issues:
-------------
- The shader code is still messy, I'd like to clean it up a bit more;
- The Gas giant II looks smaller than it does originally. That has been a design decision, as the original
render of it was trimming the outer ring, while holding the planet well in focus. However, I believe that
the priority is the complete rendering of the planet WITH the intact ring and the implemented is free to
resize the whole thing, so given the viewportin this project is a fixed one, this is the way it's staying.
I have, however, included an experimental Scale modifier, to allow zooming in to the planet. Will also
have to fix the pixelated ring;
- The Star is not fully implemented yet, given that the flares pose a similar problem as to the Gas giant II
(see above), I'll probably implement something similar, by reducing the star size;
- Clouds tend to dither in a weird way for some planets. Most noticeably the IceWorld, whose clouds sometimes
get garbled in a smaller mess of pixels with holes in them. Not sure where that comes from, probably
another platform-dependent way of interpreting API functions. Not important for now;

Planed features/work
--------------------
- Seed generator to populate parameters procedurally, nicer than blind random;
- Further clean-up/refactor code;
- Finish the star code;
- Try and fix a bug that makes the shading of the light weird on a planet. Pixels aren't square there if you zoom;
- Png export for:
	- texture atlases and json sprite pointers;
	- layered data, such as cloud rendered separately from planets;
- Implement color params edit. Probably at first manually from the json, later in the UI somehow, if it's not
too much work;
- Refactoring of shaders, trying to make best use of common math across all shaders;
- Implement separate light points for each celestial body. For some of them, the general light position does not work;