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author= Mark Moxon;
description= Fully documented source code disassembly for Acornsoft Aviator on the BBC Micro, with lots of deep dive articles explaining how every aspect of the game works.;
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Text of the page (random words):
ology site to find out more about the tools i use aviator written by geoffrey j crammond acornsoft 1983 commentary mark moxon 2021 all rights reserved home page using this site home page start at the very beginning quick start guide all you need to know to start exploring this site all about this project project history building the source and more all about this project about this project the story of how this project came to be terminology used in this commentary read this before you explore the source code building aviator from the source how to build your own working copy of aviator useful links a collection of links to pages i ve found useful during this project acknowledgements the giants on whose shoulders this project stands site history a short history of this site s development site map a top level map of this website to do list code that could benefit from a bit more analysis playing with the aviator source code playing aviator in the 21st century how to play all the versions of aviator analysed here deep dive articles over 30 articles on how aviator weaves its magic index index of all deep dive articles discover how aviator works under the hood deep dives 3d geometry matrices lines points objects and visibility 3d geometry lines and points the fundamental elements of aviator s 3d world 3d objects how aviator manages trees hills aliens towns and other 3d objects placing objects on the map reconstructing the game s map from the data in the game code rotation matrices the four matrices that lie at the heart of aviator s 3d model rotating and translating points in 3d space converting between different frames of reference in 3d visibility checks deciding which lines to draw on screen and which to hide flight model simulating the forces on a flying aircraft flight model the flight model the maths behind the spitfire s aerodynamic flight simulation matching the code to the flight model tracking down the flight model features that are mentioned in the manual stalling and recovery how aviator simulates a stalling plane and the recovery process ripping the wings off modelling the high g forces that can rip the wings clean off take offs and landings the two most important and dangerous parts of every flight on ground calculations the calculations behind the plane s behaviour on the ground flying skills flying under bridges and over main street dashboard the spitfire s many dials and indicators dashboard clock hands and dial indicators drawing the clock like indicators on the dashboard hard coded division in the dashboard routines using hand tailored division code for fast calculations the theme aliens bullets and everything in between the theme alien feeding and growth patterns the many stages of the alien life cycle aliens attack acornsville planning an alien attack on civilisation adding bullets to the world spawning bullets that leave tracer trails in the sky detecting alien hits the geometry behind aliens and their weak spots explosions and turbulence destroying aliens at close range can have serious consequences graphics smooth animation and the drawing routines graphics flicker free animation through colour cycling using four colours to create super smooth animated graphics converting pixel coordinates to screen addresses going from x y coordinates to screen memory addresses line buffers caching line information for faster erasing main loop the main game loop and task scheduler main loop program flow of the main game loop the sequence of events in the main game loop scheduling tasks in the main loop how aviator does the right thing at the right time maths multiplication trigonometry and random numbers maths times tables and nibble arithmetic inside aviator s multiplication algorithms trigonometry calculating sine and cosine in the rotation matrices random numbers how aviator generates random numbers miscellaneous key loggers and code secrets miscellaneous the key logger making sure that every key press makes gets recorded multi byte variables how aviator stores multi byte variables source code clues hidden in the game binary snippets of original source code and what they can tell us exploring the aviator source code aviator source code annotated source of bbc micro aviator version information about the version of aviator on this site details of the different versions of aviator aviator source code by file map of the source code an overview of how the source code for aviator is structured annotated source files the fully commented source files aviator source files workspaces and configuration the main variable workspaces used in aviator aviator a source part 1 of the main game code aviator b source part 2 of the main game code aviator c source part 3 of the main game code aviator d source part 4 of the main game code aviator e source part 5 of the main game code aviator f source part 6 of the main game code aviator source code by category 3d geometry rotation matrices coordinate transformations object calculations and more subroutines addpointtoobject add a point vector to an object s coordinates addtemptopoint part 1 of 2 add the xtemp1 vector to a point store the result in another point and set the result to hidden if it overflows addtemptopoint part 2 of 2 check whether the vector addition overflowed and set the point s visibility accordingly nextobjectgroup cycle to the next object group projectaxisangle convert the rotation angles of the plane into coordinates projectpoint part 1 of 3 project a point onto the screen i e convert from 3d coordinates to screen coordinates projectpoint part 2 of 3 calculate the screen coordinates of the projected point projectpoint part 3 of 3 move the projected coordinates to the centre of the screen and update the point s status byte setmatrices set up matrices 1 to 4 setmatrixentry calculate a matrix entry setobjectcoords part 1 of 11 calculate the coordinates for an object s location setobjectcoords part 2 of 11 pre process the bullets objects 12 13 14 or 15 setobjectcoords part 3 of 11 logic for checking which objects to pre process setobjectcoords part 4 of 11 pre process the object groups objects 6 7 8 or 9 setobjectcoords part 5 of 11 logic for checking which objects to pre process setobjectcoords part 6 of 11 pre process dormant aliens object group 30 setobjectcoords part 7 of 11 pre process feeding and flying aliens objects 31 32 and 33 setobjectcoords part 8 of 11 process the object setobjectcoords part 9 of 11 process the next object in the group if applicable or return from the subroutine if not setobjectcoords part 10 of 11 process the next dormant alien object group 30 setobjectcoords part 11 of 11 update the object status and return from the subroutine setobjecttoorigin set an object s coordinates to 0 0 0 setobjpointcoords part 1 of 2 calculate the coordinate for a point within an object setobjpointcoords part 2 of 2 apply the correct scale factor to the matrix multiplication setpoint set a point s coordinates to the value a a a setpointcoords calculate the coordinates for a point setpointtoorigin set a point s coordinates to the origin at 0 0 0 setpointvisibility set the status byte for multiple points to indicate that their coordinates and visibility have been calculated variables groupstart the starting value for each object s group number lineendpointid the point id for a line s end point linestartpointid the point id for a line s start point numberoflines the total number of lines in aviator s 3d world objectgroup the current group number for object ids 6 7 8 and 9 objectpoints sequences of related points that together make up objects xgravityhi high byte of point 253 x coordinate xgroupobjecthi high byte of the x coordinate for objects in a group 6 to 9 xlinearhi high byte of point 252 x coordinate xobjecthi high byte of the x coordinate for an object xobjectlo low byte of the x coordinate for an object xobjectpoint scaled x coordinates of the points that make up objects relative to the object s anchor point xpointhi high byte of the x coordinate for a point xtemppoint1hi high byte of point 254 x coordinate xtemppoint2hi high byte of point 255 x coordinate yobjecthi high byte of the y coordinate for an object yobjectlo low byte of the y coordinate for an object yobjectpoint scaled y coordinates of the points that make up objects relative to the object s anchor point zgroupobjecthi high byte of the z coordinate for objects in a group 6 to 9 zobjecthi high byte of the z coordinate for an object zobjectlo low byte of the z coordinate for an object zobjectpoint scaled z coordinates of the points that make up objects relative to the object s anchor point zpointhi high byte of the z coordinate for a point dashboard dials indicators radars and flight controls subroutines artificialhorizon vector line calculation for the artificial horizon on indicator 7 drawfuelpixel draw or erase a pixel on the fuel gauge on the dashboard drawradarblip draw a blip on the radar runway or alien gethandvector vector line calculation for a hand on indicators 0 to 6 getradarvector calculate the radar line vector for a line the runway or a dot an alien indicatorb update the brakes indicator b indicatorf update the flaps indicator f and related variables indicatort update the theme indicator t indicatoru update the undercarriage indicator u and related variables resetradar reset the radar display showupsidedownbar show or hide the upside down bar in the artificial horizon indicator updatedashboard update two indicators on the dashboard one from 0 6 one from 7 11 cycling through them with each subsequent call updatefuelgauge update the fuel gauge every 16 iterations of the main loop updateindicator part 1 of 15 update a single indicator on the dashboard updateindicator part 2 of 15 calculations for the compass indicator 0 updateindicator part 3 of 15 calculations for the airspeed indicator indicator 1 updateindicator part 4 of 15 calculations for the altimeter s small hour hand indicator 2 updateindicator part 5 of 15 calculations for the altimeter s minute hand indicator 3 updateindicator part 6 of 15 logic for checking which indicator to update updateindicator part 7 of 15 calculations for the vertical speed indicator indicator 4 updateindicator part 8 of 15 logic for checking which indicator to update updateindicator part 9 of 15 calculations for the turn indicator indicator 5 the bottom part of the slip and turn indicator updateindicator part 10 of 15 calculations for the slip indicator indicator 6 the top part of the slip and turn indicator updateindicator part 11 of 15 calculations for the artificial horizon indicator 7 updateindicator part 12 of 15 logic for checking which indicator to update updateindicator part 13 of 15 calculations for the rudder indicator indicator 9 updateindicator part 14 of 15 calculations for the joystick position display indicator 8 or 10 updateindicator part 15 of 15 calculations for the thrust indicator indicator 11 updateradarblip update a blip on the radar runway or alien variables altitudeminutes the value of the altimeter s large minute hand dialquadrant the value range of a quadrant in each indicator indicator0to6 the first indicator counter indicator7to11 the second indicator counter indicatorbase the base value for each indicator indicatorlinei line buffer storage for the start x coordinate for each indicator line i indicatorlinej line buffer storage for the start y coordinate for each indicator line j indicatorlinet line buffer storage for the indicator line s x delta t indicatorlineu line buffer storage for the indicator line s y delta u indicatorlinev line buffer storage for the indicator line s direction v indicatormax the maximum value shown on each indicator indicatormin the minimum value shown on each indicator joycoord temporary storage previouscompass stores the value of the compass heading when we draw the runway on the radar so we can erase the line later xdeltamax the maximum x delta for the hand line in each indicator xjoycoord temporary storage xradarbuffer the x coordinates of the runway and alien on the radar ydeltamax the maximum y delta for the hand line in each indicator yjoycoord temporary storage yradarbuffer the y coordinates of the runway and alien on the radar drawing lines the core line drawing routines subroutines clipbestendofline clip a line at the start or end point depending on which is best clipstartofline part 1 of 5 check whether the line is completely off screen clipstartofline part 2 of 5 work out the deltas depending on the direction of slope clipstartofline part 3 of 5 work out the deltas depending on the steepness of slope clipstartofline part 4 of 5 calculate where to clip the line clipstartofline part 5 of 5 move the start point to the clipped position and return it drawcanopyline part 1 of 9 draw a line in the canopy view drawcanopyline part 2 of 9 modify the line drawing routine for a shallow horizontal slope drawcanopyline part 3 of 9 draw a line as a shallow horizontal slope drawcanopyline part 4 of 9 draw a part of the line working down the screen drawcanopyline part 5 of 9 draw a part of the line working up the screen drawcanopyline part 6 of 9 draw a part of the line working along the screen drawcanopyline part 7 of 9 modify the line drawing routine for a steep vertical slope drawcanopyline part 8 of 9 draw a line as a steep vertical slope drawcanopyline part 9 of 9 if the line was clipped draw a line from the clipped coordinates to the edge of the screen drawclippedline part 1 of 6 clip a line to fit on screen starting with the line deltas drawclippedline part 2 of 6 work out whether the line s start point is on screen drawclippedline part 3 of 6 work out whether the line s end point is on screen drawclippedline part 4 of 6 calculate the starting point and direction for our clipped vector line drawclippedline part 5 of 6 calculate the deltas for our clipped vector line drawclippedline part 6 of 6 add the clipped line to the line buffer and draw it drawhalfhorizon draw half of the horizon line drawindicatorbar draw a vertical bar on indicator 9 rudder or 11 thrust drawindicatorhand apply min and max limits to an indicator value and draw a hand on the indicator drawindicatorline draw a line on indicators 0 to 7 i e a dial hand 0 6 or an artificial horizon 7 drawjoystickcross draw a cross in the joystick position display indicator 8 or 10 drawortholine draw an orthogonal line i e vertical or horizontal drawvectorline part 1 of 3 draw a line set up pixel bytes and slope variables drawvectorline part 2 of 3 calculate the coordinates of the next pixel as we step along the line by one pixel drawvectorline part 3 of 3 plot a pixel at i j erasecanopylines draw all the lines from a line buffer to erase them modifydrawroutine modify the drawing routines to draw in the correct colour for the current colour cycle swaplinepoints copy an end point into a start point variables colour1l2r pixel bytes for dr...
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