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{{Canvas Navigation}}
    
== Objective ==
 
== Objective ==
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Demonstrate how to modify/animate liveries using Nasal/Canvas.
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{{FGCquote
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  |The code is already in place for the "dirtying" effect - it's a fairly simple linear introduction of the dirt texture, becoming less transparent the more the aircraft flies without being washed. Being washed also includes rain - continued exposure to precipitation will "wash away" dirt by making the dirt layer more transparent according to the heaviness of the weather. It's been tried on the APU smudge, and whilst the values will need to be tweaked, it already works pretty much to my expectations and satisfaction.
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  |{{cite web |url=http://forum.flightgear.org/viewtopic.php?p=218792#p218792
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    |title=<nowiki>Re: Two Images to a Texture</nowiki>
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    |author=<nowiki>Algernon</nowiki>
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    |date=<nowiki>Wed Sep 17</nowiki>
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  }}
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}}
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{{FGCquote
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  |But in the long-term, I would prefer turning this into a Nasal class that can manage multiple Canvases per aircraft, so that we can also re-implement the existing livery system accordingly, so that it stops interfering with canvas. Which would also mean that people can reuse the same class for placing bullet holes or doing other fancy things (e.g. [[Immatriculation]])
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  |{{cite web |url=http://forum.flightgear.org/viewtopic.php?p=218789#p218789
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    |title=<nowiki>Re: Two Images to a Texture</nowiki>
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    |author=<nowiki>Hooray</nowiki>
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    |date=<nowiki>Wed Sep 17</nowiki>
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  }}
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}}
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== Proof of Concept: Exhaust dirt ==
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''by [[User:Algernon|Algernon]] ([[User talk:Algernon|talk]]) 17:09, 17 September 2014 (UTC) ''
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To document the implementation on a FlightGear aircraft from the aircraft developer's point of view, I've chosen one of my pet projects, the Eurofighter EF2000 V2.0 which will be released in early 2015.
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The intention is to use Canvas to allow multiple textures per livery, in this case those textures being the original livery paintwork and another, alpha-transparent texture consisting of dirt streaks specifically added to the livery paintwork to match with vents, seams and other sources of grimy build-ups. The intention is to allow dynamic management of the transparency of the dirt layer according to time and exposure to various elements, maintaining compatibility with the standard livery switching method and working similarly whether Rembrandt is enabled or not.
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<gallery mode="packed">
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Two-layers.jpg|The two textures concerned, the ASG paintwork and the separate alpha transparency with dirt streaks
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Dynamic-Textures-First-Try.jpg|A first (failed) attempt to put a canvas onto a model object in place of its texture.
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Ef2000dyn1.jpg|The EF2000 showing a dynamically-changed texture on the fuselage - at the moment, the resolution appears to be wrong and the UV coordinates seem to be being ignored.
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File:Ef2000dyn2.jpg|Changing the dialog window size to be the same size as the texture fixed the issue - note that the fuselage sections are free of dirt (except the APU exhaust smudge, which is a special case) where as the wings and tail have integral dirt in the texture.
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File:Ef2000dyn3.jpg|A full-screen illustration using the updated Canvas code to make the canvas independent of the window, but with the window still displaying the canvas. Here, only the base "clean" paintwork texture is added to the fuselage element.
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File:Ef2000dyn4.jpg|After creating a canvas with the base "clean" paintwork texture, another child is added containing the dirt layer transparency. The effect is seen both in the dialog window and on the airframe.
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</gallery>
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''This section will be updated as the implementation continues.''
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=== Model Work ===
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To start with, I cloned the EF2000's model and made a copy called "EF2000-canvas.ac", cloned the model XML file in the same way, and changed the paths appropriately to create a completely separate model for this experiment. The model objects which will be subject to the dynamic effects - effectively, the painted surfaces - were isolated from items like the canopy glass, gear and engines and given the same material, named '''CanvasPaint''' and consisting of an image texture: a livery in Air Superiority Grey but without the dirt layer already included. My first experiment will be to create a canvas and try to apply it to the mesh.
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{{-}}
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=== Canvas Code ===
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From the code snippets above and [[Howto:Using raster images and nested canvases]], I've put together my first attempt at some Canvas code. It appears that the canvas is the right size, and both .jpg and .png textures are loaded. But the placement line did not seem to make any difference to the texture on the named model object ("Fuselage"). When the native XML/Nasal livery object was commented out, the image was successfully displayed on the fuselage, but incorrectly sized and apparently without UV mapping (see image below).
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<syntaxhighlight lang="nasal">
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# Create a standalone Canvas (not attached to any GUI dialog/aircraft etc)
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var myCanvas = canvas.new({
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  "name": "Livery Test",  # The name is optional but allow for easier identification
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  "size": [2048, 2048], # Size of the underlying texture (should be a power of 2, required) [Resolution]
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  "view": [2048, 2048],  # Virtual resolution (Defines the coordinate system of the canvas [Dimensions]
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                        # which will be stretched the size of the texture, required)
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  "mipmapping": 1      # Enable mipmapping (optional)
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});
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# create our top-level/root group that contains all other Canvas elements
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var root = myCanvas.createGroup();
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# Add a placement by replacing the textured face "Fuselage" in the 3D model
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# This replaces the texture on the aircraft and attaches the Canvas texture
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myCanvas.addPlacement({"node": "Fuselage"});
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# hash with all images added
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var layers = {};
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# texture path
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var path="Aircraft/EF2000/Models/";
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foreach(var image; ['EF2000.png','EF2000-dirt.png']) {
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if(contains(layers, image)) print("Warning: replacing texture (added twice): ", image);
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# Put a raster image into the canvas and save the image in a hash: layers['EF2000.png].hide();
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layers[image] = root.createChild("image")
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    .setFile( path~image )
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    .setSize(2048,2048)
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}
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# object-oriented settimer() replacement
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# see: http://wiki.flightgear.org/List_of_Nasal_extension_functions#maketimer.28.29_.282.11.2B.29
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var timer_hide = maketimer(3.0, func() {
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  layers['EF2000-dirt.png'].hide();
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});
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var timer_show = maketimer(5.0, func() {
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  layers['EF2000-dirt.png'].show();
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});
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# start those two timers to hide/show the dirt texture with 2 second delays
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timer_hide.start();
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timer_show.start();
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# Create a Canvas dialog window to hold the canvas and show that it's working
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# the Canvas is now standalone, i.e. continues to live once the dialog is closed!
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var window = canvas.Window.new([512,512],"dialog");
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window.setCanvas(myCanvas);
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</syntaxhighlight>
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Here's another slightly-restructured version (untested), to better encapsulate the concept of a "managed texture" so that the code can be reused for other aircraft/purposes, e.g. for placing bullet holes etc:
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<syntaxhighlight lang="nasal">
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var ManagedTexture = {
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# this create a new TextureManager object
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new: func(name, size, path) {
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# create a temporary object that inherits from TextureManager
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var m = {parents:[ManagedTexture]};
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# Create a standalone Canvas (not attached to any GUI dialog/aircraft etc)
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m.canvas = canvas.new({
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"name": name, # The name is optional but allow for easier identification
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"size": [size[0], size[1]], # Size of the underlying texture (should be a power of 2, required) [Resolution]
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"view": [size[0], size[1]], # Virtual resolution (Defines the coordinate system of the canvas [Dimensions]
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                        # which will be stretched the size of the texture, required)
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"mipmapping": 1      # Enable mipmapping (optional)
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});
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# create our top-level/root group that contains all other Canvas elements
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m.root = m.canvas.createGroup();
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# hash with all layers/images added
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m.layers = {};
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m.basepath = path;
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# return the new object to the caller
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return m;
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},
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replaceTexture: func(name) {
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# Add a placement by replacing the textured face specified (name) in the 3D model
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# This replaces the texture on the aircraft and attaches the Canvas texture
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m.canvas.addPlacement({"node": name});
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},
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addDynamicLayer: func(filename, callback=nil) {
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if(contains(layers, image)) print("Warning: replacing texture (added twice): ", image);
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# Put a raster image into the canvas and save the image in a hash: layers['EF2000.png].hide();
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m.layers[image] = root.createChild("image")
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    .setFile( m.basepath~image )
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    .setSize(2048,2048)
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return m.layers[image];
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},
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}; # of ManagedTexture
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# now, create a new managed texture, specifying the path to use for texture lookups
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var ExhaustDirt = ManagedTexture.new( name:"ExhaustDirt",
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size:[2048,2048],
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path:'Aircraft/EF2000/Models/' );
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ExhaustDirt.replaceTexture('Fuselage');
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# Create a Canvas dialog window to hold the canvas and show that it's working
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# the Canvas is now standalone, i.e. continues to live once the dialog is closed!
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var window = canvas.Window.new([512,512],"dialog");
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window.setCanvas(ExhaustDirt.canvas);
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foreach(var layer; [ {file:'EF2000.png'},
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{file:'EF2000-dirt.png'} ]) {
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ExhaustDirt.addDynamicLayer(layer.file);
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}
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var timer_hide = maketimer(3.0, func() {
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  ExhaustDirt.layers['EF2000-dirt.png'].hide();
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});
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var timer_show = maketimer(5.0, func() {
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  ExhaustDirt.layers['EF2000-dirt.png'].show();
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});
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# start those two timers to hide/show the dirt texture with 2 second delays
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timer_hide.start();
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timer_show.start();
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</syntaxhighlight>
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== Original Example ==
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{{Note|This assumes that you're using the ogel aircraft and that the face texture can be looked up using the name '''Head'''.
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The map shown here is just an example, this could obviously be anything, including raster/svg images, custom OpenVG/ShivaVG paths, osgText etc.
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To implement a dirt texture, you'd want to use the corresponding texture ID and then overlay a static dirt texture using some kind of random scheme, e.g. by adding texture maps/sub regions to the exhaust area. See [[Canvas Image]] for details.
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In its current form, this will simply apply the texture mapping used in the 3D mode "as is". In other words, all texture-mapped faces should be accessible from Nasal/Canvas and can be modified/animated.
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In comparison to a pure shader-based approach this is likely to have a little more overhead, while not requiring effects/shaders (but RTT/FBOs due to Canvas) - also, this approach is agnostic to the underlying rendering pipeline, i.e. should also work for Rembrandt aircraft, without having to be customized.  }}
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[[File:Canvas-livery-demo-using-ogle.png|left|400px|A screen shot showing the ogel aircraft whose livery is dynamically changed using the [[Canvas]] system - in this case, we're simply rendering a [[MapStructure]] map onto the face of the pilot using ~10 lines of Nasal/Canvas code.]]
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<syntaxhighlight lang="nasal">
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# create a new window, dimensions are 320 x 160, using the dialog decoration (i.e. titlebar)
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var window = canvas.Window.new([320,160],"dialog");
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# adding a canvas to the new window and setting up background colors/transparency
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var myCanvas = window.createCanvas();
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# creating the top-level/root group which will contain all other elements/group
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var root = myCanvas.createGroup();
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# add a new placement using a texture identifier (see $FG_ROOT/ogel/Models/SinglePiston.ac or existing liveries)
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myCanvas.addPlacement({"node": "Head"});
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# now, let's add some content to our canvas (this could be really anything)
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# animations are handled via timers/listeners (not shown here, hidden in the depths of MapStructure)
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var TestMap = root.createChild("map");
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TestMap.setController("Aircraft position");
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TestMap.setRange(25);
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TestMap.setTranslation(    myCanvas.get("view[0]")/2,
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                          myCanvas.get("view[1]")/2
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                        );
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var r = func(name,vis=1,zindex=nil) return caller(0)[0];
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foreach(var type; [r('APT'), r('VOR') ] )
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TestMap.addLayer(factory: canvas.SymbolLayer, type_arg: type.name, visible: type.vis, priority: type.zindex,);
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</syntaxhighlight>
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== Background ==
 
{{FGCquote
 
{{FGCquote
 
   |Does anyone know if it's possible for FG to work with a texture which consists of two images, and manipulate those images seperately? The application here is airframe dirt - I'm trying to find out if I can have one texture for the aircraft livery, and another for accumulated dirt, which would gradually become less transparent as the airframe hours increase. I am aware of the questionable advisability of using alpha channels excessively in FG, this is just an experiment at the moment.  
 
   |Does anyone know if it's possible for FG to work with a texture which consists of two images, and manipulate those images seperately? The application here is airframe dirt - I'm trying to find out if I can have one texture for the aircraft livery, and another for accumulated dirt, which would gradually become less transparent as the airframe hours increase. I am aware of the questionable advisability of using alpha channels excessively in FG, this is just an experiment at the moment.  
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   }}
 
   }}
 
}}
 
}}
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[[Category:Canvas]]
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[[Category:Aircraft enhancement]]

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