#2: the original

Source description for demo by Marijn Haverbeke.

// see http://marijn.haverbeke.nl/js1k.html for more context // the abbreviation loop, initializing the variabled needed by the key-handlers on the side. for(prop in context=canvas.getContext('2d')) context[prop[jump=speed_x=speed_y=0]+(prop[6]||'')]=context[prop]; setInterval(function(){ if(dead) // initialize the player position, score, and heightmap for(x=405,i=y=score=0;i<1e4;) // (screen_width is reused as the off-the-screen height of gap blocks) // a block can be a gap if its index is <9, or if the last block was no gap. after this test, // a random number is compared to .3 to determine whether an actual gap is generated, or a // regular random height. last_height=heights[i++]= i<9|last_height<screen_width&Math.random()<.3?screen_width:Math.random()*unit+80|0; // silly formula to create parabolic movement based on the time plant_pos=++time%99-unit;plant_pos=plant_pos*plant_pos/8+20; y+=speed_y; // only move horizontally if that doesn't take us deep underground (x/unit|0 fetches the index of // the block below an x coordinate) x+=y-heights[(x+speed_x)/unit|0]>9?0:speed_x; // compute final player height index, and ground level under it ground=heights[player_index=x/unit|0]; // adjust y and speed_y based on whether we are on the ground or not speed_y=y<ground|speed_y<0?speed_y+1:(y=ground,jump?-10:0); // we'll need the context a lot with(context){ A=function(color,x,y,radius){ // a is the abbreviated form of arc radius&&a(x,y,radius,0,7,0); // if color is not a gradient object (we set a P property in gradient objects), it is an index // into a set of colors fillStyle=color.P?color:'#'+'ceff99ff78f86eeaaffffd45333'.substr(color*3,3); // f for fill, ba for beginPath f(); ba(); }; // now loop over visible, or close to visible, blocks, and draw them and their clouds for(dead=i=0;i<21;i++){ // this loop is reused for drawing the background/rainbow, which consists of seven concentric // circles. there's no good reason why interleaving clearing the screen with drawing the // screen's contents should work, but in this case it does i<7&&A(i%6,screen_width/2,235,i?250-15*i:screen_width); // we start drawing 5 units in front of the player (first four will be off-screen, needed just // for clouds) height_index=player_index-5+i; scroll_pos=x-height_index*unit; // since player screen position is fixed, we can use scroll position for collision detection. // this variable indicates whether the player is in the 'middle' of the current block player_in_middle=scroll_pos>9&scroll_pos<41; // ta for translate. move to start of block to make other drawing commands shorter ta(unit-scroll_pos,0); // cL for createLinearGradient, for the ground/grass gradient gradient=cL(0,height=heights[height_index],0,height+9); // if height is divisible by 6, there's a coin here. draw it. if the player is standing on the // ground, in the middle of this unit, pick up the coin height%6||(A(2,25,height-7,5),y^ground||player_in_middle&&(heights[height_index]-=.1,score++)); // abbreviate, since we need this twice (and use it again to test whether a value passed to A // is a gradient) gradient.P=gradient.addColorStop; // this implements sinky terrain---when the index is divisible by 7, we use a different color, // and do the sinking if the player is standing here gradient.P(0,height_index%7?'#5e1':(height_index^player_index||y^height|| (y=heights[height_index]+=plant_pos/99),'#a59')); // brown earth color for the bottom of the gradient gradient.P(1,'#b93'); // this draws the clouds height_index%4&&A(6,time/2%200,9,height_index%2?27:33); // draws the terrain block. m is moveTo, qt is quadraticCurveTo, l is lineTo m(-6,screen_height);qt(-6,height,3,height);l(47,height);qt(56,height,56,screen_height);A(gradient); // draw deco trees or piranha plant (height==screen_width for gap blocks), check for collision // with plant height_index%3?0:height<screen_width ?(A(gradient,33,height-15,10),fc(31,height-7,4,9)) :(A(7,25,plant_pos,9),A(3,25,plant_pos,5),fc(24,plant_pos,2,screen_height), dead=player_in_middle&y>plant_pos-9?1:dead); // undo block-local translation ta(scroll_pos-unit,0) } // draws the player, using the speed to adjust the position of the iris A(6,unit,y-9,11); A(5,iris_x=unit+speed_x*.7,iris_y=y-9+speed_y/5,8); A(8,iris_x,iris_y,5); // color is already dark from eye pupil, draw score with this color fx(score+'ยข',5,15) } // check whether the player has fallen off the screen dead=y>screen_height?1:dead },unit); onkeydown=onkeyup=function(e){ // if this is a keydown event, new_val gets the value 4, otherwise 0 new_val=e.type[5]?4:0; e=e.keyCode; // give jump a truthy value if up was pressed, falsy if up was released jump=e^38?jump:new_val; // similar for speed_x, inverting new_val if left is pressed speed_x=e^37?e^39?speed_x:new_val:-new_val }