HTML5 Terry Cavanagh’s vvvvvv game prototype
Talking about vvvvvv game, Game development, HTML5 and Javascript.
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One platform I really love is Terry Cavanagh‘s vvvvvv (six “v” in a row), in my opinion one of the most playable games of its genre since Jet Set Willy has been released.
It’s a platform game but you cannot jump: instead, you can switch the gravity which affects the player so you can walk both on the floor and on the ceiling.
To create this interesting kind of movement, I will start from the prototype I uploaded last week: Creation of an HTML5 tile based platform game with no engines behind: pure code!
It’s pure javascript, so you won’t need any gramework or game engine to have your game up and running.
The code is fully commented and new lines are highlighted, anyway we need two steps:
MAKING THE HERO SMALLER THAN A TILE
This is necessary when we want the hero to be able to easily move into one tile sized tunnels.
The main script does not change, we only have to adjust a bit collision detection when we check for right and bottom walls. Left and upper walls collision code remain intact because in our case the hero has the origin at (0,0).
Here is the script:
(function(){
var canvas = document.getElementById("canvas"); // the canvas where game will be drawn
var context = canvas.getContext("2d"); // canvas context
var levelCols=11; // level width, in tiles
var levelRows=9; // level height, in tiles
var tileSize=32; // tile size, in pixels
var playerCol=5; // player starting column
var playerRow=4; // player starting row
var playerSize=24; // player size
var sizeDiff=tileSize-playerSize; // difference between player and tile size
var leftPressed=false; // are we pressing LEFT arrow key?
var rightPressed=false; // are we pressing RIGHT arrow key?
var upPressed=false; // are we pressing UP arrow key?
var downPressed=false; // are we pressing DOWN arrow key?
var movementSpeed=3; // the speed we are going to move, in pixels per frame
var playerXSpeed=0; // player horizontal speed, in pixels per frame
var playerYSpeed=0; // player vertical speed, in pixels per frame
var level = [ // the 11x9 level - 1=wall, 0=empty space
[1,1,1,1,1,1,1,1,1,1,1],
[1,1,0,0,0,0,0,0,0,1,1],
[1,0,0,0,0,0,0,0,0,0,1],
[1,0,0,0,1,0,1,0,0,0,1],
[1,0,0,0,0,0,0,0,0,0,1],
[1,0,0,0,1,0,1,0,0,0,1],
[1,0,0,0,0,0,0,0,0,0,1],
[1,1,0,0,0,0,0,0,0,1,1],
[1,1,1,1,1,1,1,1,1,1,1]
];
var playerYPos=playerRow*tileSize+sizeDiff/2; // converting Y player position from tiles to pixels
var playerXPos=playerCol*tileSize+sizeDiff/2; // converting X player position from tiles to pixels
canvas.width=640; // canvas width. Won't work without it even if you style it from CSS
canvas.height=480; // canvas height. Same as before
// simple key listeners
document.addEventListener("keydown", function(ev){
switch(ev.keyCode){
case 65:
leftPressed=true;
break;
case 87:
upPressed=true;
break;
case 68:
rightPressed=true;
break;
case 83:
downPressed=true;
break;
}
}, false);
document.addEventListener("keyup", function(ev){
switch(ev.keyCode){
case 65:
leftPressed=false;
break;
case 87:
upPressed=false;
break;
case 68:
rightPressed=false;
break;
case 83:
downPressed=false;
break;
}
}, false);
// function to display the level
function renderLevel(){
// clear the canvas
context.clearRect(0, 0, canvas.width, canvas.height);
// walls = red boxes
context.fillStyle = "#ff0000";
for(i=0;i<levelRows;i++){
for(j=0;j<levelCols;j++){
if(level[i][j]==1){
context.fillRect(j*tileSize,i*tileSize,tileSize,tileSize);
}
}
}
// player = green box
context.fillStyle = "#00ff00";
context.fillRect(playerXPos,playerYPos,playerSize,playerSize);
}
// this function will do its best to make stuff work at 60FPS - please notice I said "will do its best"
window.requestAnimFrame = (function(callback) {
return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame ||
function(callback) {
window.setTimeout(callback, 1000/60);
};
})();
// function to handle the game itself
function updateGame() {
// no friction or inertia at the moment, so at every frame initial speed is set to zero
playerXSpeed=0;
playerYSpeed=0;
// updating speed according to key pressed
if(rightPressed){
playerXSpeed=movementSpeed
}
else{
if(leftPressed){
playerXSpeed=-movementSpeed;
}
else{
if(upPressed){
playerYSpeed=-movementSpeed;
}
else{
if(downPressed){
playerYSpeed=movementSpeed;
}
}
}
}
// updating player position
playerXPos+=playerXSpeed;
playerYPos+=playerYSpeed;
// check for horizontal collisions
var baseCol = Math.floor(playerXPos/tileSize);
var baseRow = Math.floor(playerYPos/tileSize);
var colOverlap = playerXPos%tileSize>sizeDiff;
var rowOverlap = playerYPos%tileSize>sizeDiff;
if(playerXSpeed>0){
if((level[baseRow][baseCol+1] && !level[baseRow][baseCol] && colOverlap) || (level[baseRow+1][baseCol+1] && !level[baseRow+1][baseCol] && rowOverlap && colOverlap)){
playerXPos=baseCol*tileSize+sizeDiff;
}
}
if(playerXSpeed<0){
if((!level[baseRow][baseCol+1] && level[baseRow][baseCol]) || (!level[baseRow+1][baseCol+1] && level[baseRow+1][baseCol] && rowOverlap)){
playerXPos=(baseCol+1)*tileSize;
}
}
// check for vertical collisions
var baseCol = Math.floor(playerXPos/tileSize);
var baseRow = Math.floor(playerYPos/tileSize);
var colOverlap = playerXPos%tileSize>sizeDiff;
var rowOverlap = playerYPos%tileSize>sizeDiff;
if(playerYSpeed>0){
if((level[baseRow+1][baseCol] && !level[baseRow][baseCol] && rowOverlap) || (level[baseRow+1][baseCol+1] && !level[baseRow][baseCol+1] && colOverlap && rowOverlap)){
playerYPos = baseRow*tileSize+sizeDiff;
}
}
if(playerYSpeed<0){
if((!level[baseRow+1][baseCol] && level[baseRow][baseCol]) || (!level[baseRow+1][baseCol+1] && level[baseRow][baseCol+1] && colOverlap)){
playerYPos = (baseRow+1)*tileSize;
}
}
// rendering level
renderLevel();
// update the game in about 1/60 seconds
requestAnimFrame(function() {
updateGame();
});
}
updateGame();
})();
And this is the result
Move the hero with WASD keys and you will be able to easily walk in and out of the center of the stage, in the middle of the four blocks.
Now we have to add gravity.
ADDING AND FLIPPING PLAYER GRAVITY
In order to create gravity, we first need to disable UP and DOWN movement, and in this case we will assign UP arrow key the function to switch gravity.
Gravity acts as an acceleration on the player, and we will also set a maximun free fall speed for a gaming experience purpose. We don’t want the player to fall too fast, like it would happen in a real world.
Since the gravity wins on every other force, this time we’ll need to give vertical collisions a priority over horizontal collisions, so I am checking for horizontal collisions after I managed vertical collisions.
Here is the script:
(function(){
var canvas = document.getElementById("canvas"); // the canvas where game will be drawn
var context = canvas.getContext("2d"); // canvas context
var levelCols=11; // level width, in tiles
var levelRows=9; // level height, in tiles
var tileSize=32; // tile size, in pixels
var playerCol=5; // player starting column
var playerRow=4; // player starting row
var playerSize=24; // player size
var sizeDiff=tileSize-playerSize; // difference between player and tile size
var leftPressed=false; // are we pressing LEFT arrow key?
var rightPressed=false; // are we pressing RIGHT arrow key?
var upPressed=false; // are we pressing UP arrow key?
var downPressed=false; // are we pressing DOWN arrow key?
var movementSpeed=3; // the speed we are going to move, in pixels per frame
var playerXSpeed=0; // player horizontal speed, in pixels per frame
var playerYSpeed=0; // player vertical speed, in pixels per frame
var gravityForce=0.5; // gravity acceleration, in pixels per frame per frame
var maxFallingSpeed=10; // maximum falling speed
var level = [ // the 11x9 level - 1=wall, 0=empty space
[1,1,1,1,1,1,1,1,1,1,1],
[1,1,0,0,0,0,0,0,0,1,1],
[1,0,0,0,0,0,0,0,0,0,1],
[1,0,0,0,1,0,1,0,0,0,1],
[1,0,0,0,0,0,0,0,0,0,1],
[1,0,0,0,1,0,1,0,0,0,1],
[1,0,0,0,0,0,0,0,0,0,1],
[1,1,0,0,0,0,0,0,0,1,1],
[1,1,1,1,1,1,1,1,1,1,1]
];
var playerYPos=playerRow*tileSize+sizeDiff/2; // converting Y player position from tiles to pixels
var playerXPos=playerCol*tileSize+sizeDiff/2; // converting X player position from tiles to pixels
canvas.width=640; // canvas width. Won't work without it even if you style it from CSS
canvas.height=480; // canvas height. Same as before
// simple key listeners
document.addEventListener("keydown", function(ev){
switch(ev.keyCode){
case 65:
leftPressed=true;
break;
case 87:
// this time we reverse gravity if the player is on the floor
upPressed=true;
if(playerYSpeed==0){
gravityForce*=-1;
}
break;
case 68:
rightPressed=true;
break;
case 83:
downPressed=true;
break;
}
}, false);
document.addEventListener("keyup", function(ev){
switch(ev.keyCode){
case 65:
leftPressed=false;
break;
case 87:
upPressed=false;
break;
case 68:
rightPressed=false;
break;
case 83:
downPressed=false;
break;
}
}, false);
// function to display the level
function renderLevel(){
// clear the canvas
context.clearRect(0, 0, canvas.width, canvas.height);
// walls = red boxes
context.fillStyle = "#ff0000";
for(i=0;i<levelRows;i++){
for(j=0;j<levelCols;j++){
if(level[i][j]==1){
context.fillRect(j*tileSize,i*tileSize,tileSize,tileSize);
}
}
}
// player = green box
context.fillStyle = "#00ff00";
context.fillRect(playerXPos,playerYPos,playerSize,playerSize);
}
// this function will do its best to make stuff work at 60FPS - please notice I said "will do its best"
window.requestAnimFrame = (function(callback) {
return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame ||
function(callback) {
window.setTimeout(callback, 1000/60);
};
})();
// function to handle the game itself
function updateGame() {
// no friction or inertia at the moment, so at every frame initial speed is set to zero
playerXSpeed=0;
playerYSpeed+=gravityForce;
// limiting max vertical speed
playerYSpeed=Math.min(playerYSpeed,maxFallingSpeed);
playerYSpeed=Math.max(playerYSpeed,-maxFallingSpeed);
// updating speed according to key pressed
if(rightPressed){
playerXSpeed=movementSpeed
}
else{
if(leftPressed){
playerXSpeed=-movementSpeed;
}
else{
if(upPressed){
/*playerYSpeed=-movementSpeed;*/
}
else{
if(downPressed){
/*playerYSpeed=movementSpeed;*/
}
}
}
}
// updating player position
playerXPos+=playerXSpeed;
playerYPos+=playerYSpeed;
// check for vertical collisions, got to do it first this time
var baseCol = Math.floor(playerXPos/tileSize);
var baseRow = Math.floor(playerYPos/tileSize);
var colOverlap = playerXPos%tileSize>sizeDiff;
var rowOverlap = playerYPos%tileSize>sizeDiff;
if(playerYSpeed>0){
if((level[baseRow+1][baseCol] && !level[baseRow][baseCol] && rowOverlap) || (level[baseRow+1][baseCol+1] && !level[baseRow][baseCol+1] && colOverlap && rowOverlap)){
playerYPos = baseRow*tileSize+sizeDiff;
playerYSpeed=0;
}
}
if(playerYSpeed<0){
if((!level[baseRow+1][baseCol] && level[baseRow][baseCol]) || (!level[baseRow+1][baseCol+1] && level[baseRow][baseCol+1] && colOverlap)){
playerYPos = (baseRow+1)*tileSize;
playerYSpeed=0;
}
}
// check for horizontal collisions
var baseCol = Math.floor(playerXPos/tileSize);
var baseRow = Math.floor(playerYPos/tileSize);
var colOverlap = playerXPos%tileSize>sizeDiff;
var rowOverlap = playerYPos%tileSize>sizeDiff;
if(playerXSpeed>0){
if((level[baseRow][baseCol+1] && !level[baseRow][baseCol] && colOverlap) || (level[baseRow+1][baseCol+1] && !level[baseRow+1][baseCol] && rowOverlap && colOverlap)){
playerXPos=baseCol*tileSize+sizeDiff;
}
}
if(playerXSpeed<0){
if((!level[baseRow][baseCol+1] && level[baseRow][baseCol]) || (!level[baseRow+1][baseCol+1] && level[baseRow+1][baseCol] && rowOverlap)){
playerXPos=(baseCol+1)*tileSize;
}
}
// rendering level
renderLevel();
// update the game in about 1/60 seconds
requestAnimFrame(function() {
updateGame();
});
}
updateGame();
})();
And this is the result:
Move with A and D keys, switch gravity with W.
Download the source code of the entire project.
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