使用canvas + javascript进行2D碰撞检测

Question

Hey i'm trying to implement simple game in HTML5 canvas and Javascript. My problem is that player jumps between platforms. Whenever player jumps on platform(i have array with platform positions) i turn off the gravitation so player doesn't fall on ground.Then in my update method(the one which refreshes all the time) I call another method which checks with the for loop whether player jumped on the platform position. The problem is it only works with one platform because when i add more platforms, method loops through platform positions and player falls down. Is there a way I could constantly check all the platform positions not just one at the time? My code which checks whether player is on platform

 for(i=0;i<platforms.length;i++) {
              if ((player.y <= platforms[i].y) && (player.y >= platforms[i].y - 5) && (player.x >= platforms[i].x) && (player.x <= (platforms[i].x + platforms[i].width + 10)) && (player.jumping == true)) {
                  ground = true;
                  player.jumping=false;
              }
              else if((player.y >= platforms[i].y) && (player.y <= platforms[i].y - 5) && (player.x <= platforms[i].x) && (player.x >= (platforms[i].x + platforms[i].width + 10)) && (player.jumping == false)){
                  ground=false;
              }
              if ((player.x >= platforms[i].x - 10) && (player.x <= (platforms[i].x + platforms[i].width + 10)) && (player.y <= platforms[i].y + platforms[i].height + 10) && (player.y >= platforms[i].y-5)) {
                  player.velY = 0;

              }
              if ((player.y <= platforms[i].y) && (player.x >= platforms[i].x - 10) && (player.x <= (platforms[i].x + platforms[i].width + 10)) && (ground == true)) {
                  player.y = platforms[i].y;
                  player.jumping = false;
              }
          }

Answer 1

Use a flag while you're testing all the platforms. Here's pseudo-code:

var isOnPlatform=false;

for(i=0;i<platforms.length;i++) {

    if( testPlayerIsOnThisPlatform ){ isOnPlatform=true; }

}

if(isOnPlatform){ turn off gravity };

Answer 2

You are setting various variables for the current platform (eg you set ground = true, etc) but then the for loop goes onto the next platform and immediately clobbers all the things you set for the previous platform. You don't seem to do anything to preserve the settings when you find the platform the player was on (such as breaking out of the loop, setting a flag, or something).