使用 while 循环和 if 语句处理对象不会在 x 轴上移动

Question

我正在做一个 space ship Processing 项目，当按下按键时，子弹会在 x 轴上移动，并从停止的地方继续向右移动，直到达到屏幕的宽度.一旦它到达屏幕的宽度，子弹就会再次回到 space 飞船前面的原始位置。换句话说，给人一种老街机 space 射击游戏的感觉。

我是如何尝试做到这一点的，是在 KeyPressed 循环中使用 while 和 if 语句。当 position = width 时，再次创建子弹（回到船前）；然而子弹永远不会移动。

我对处理真的很陌生，所以我不明白他们的 while 和 if 语句是如何工作的。

//bullet
int bulletP1X = mouseX+248;
int bulletP1Y =mouseY+100; 
int bulletP2X = mouseX+207;
int bulletP2Y = mouseY+100;
int bulletRextX = mouseX+215;
int bulletRextY = mouseY+95;
int bulletT1X = mouseX+240;
int bulletT1Y = mouseY+100;
int bulletT2X = mouseX+215;
int bulletT2Y = mouseY+100;

void setup(){

size(1300,810);  

}

void draw(){
background(0,0,0);
fill(121,17,17);
strokeWeight(1);
stroke(0,0,0);

triangle(mouseX+20,mouseY+50,mouseX+20,mouseY+150,mouseX+200,mouseY+100);
fill(255,255,210);
triangle(mouseX+150,mouseY+87,mouseX+150,mouseY+113,mouseX+200,mouseY+100);

//Left wing of Space Ship
beginShape();
stroke(255,255,255);
fill(121,17,17);
vertex(mouseX+20,mouseY+50);
vertex(mouseX+40,mouseY+40);
vertex(mouseX+200,mouseY+95);
vertex(mouseX+200,mouseY+105);
endShape();

//Right wing of Space Ship
beginShape();
stroke(255,255,255);
fill(121,17,17);
vertex(mouseX+20,mouseY+150);
vertex(mouseX+40,mouseY+160);
vertex(mouseX+200,mouseY+105);
vertex(mouseX+200,mouseY+100);
endShape();

//Inside white banner of Space Ship (top)
beginShape();
stroke(255,255,255);
fill(255,255,255);
vertex(mouseX+20,mouseY+65);
vertex(mouseX+55,mouseY+85);
vertex(mouseX+150,mouseY+90);
vertex(mouseX+150,mouseY+100);
vertex(mouseX+20,mouseY+100);
endShape();

//Inside white banner of Space Ship (bottom)
beginShape();
vertex(mouseX+20,mouseY+135);
vertex(mouseX+55,mouseY+115);
vertex(mouseX+150,mouseY+112);
vertex(mouseX+150,mouseY+100);
vertex(mouseX+20,mouseY+100);
endShape();

//White back of ship behind the cockpit
beginShape();
fill(255,255,255);
vertex(mouseX+5,mouseY+80);
vertex(mouseX+20,mouseY+65);
vertex(mouseX+20,mouseY+135);
vertex(mouseX+5,mouseY+115);  
endShape();

fill(0,0,0);
ellipse(mouseX+30,mouseY+100,30,20);
ellipse(mouseX+60,mouseY+70,10,10);
ellipse(mouseX+60,mouseY+130,10,10);
stroke(0,0,0);

//square shapes inside ship
fill(255,255,255);
stroke(0,0,0);
rect(mouseX+100,mouseY+95,50,10);
rect(mouseX+105,mouseY+98,40,4);

//line design inside white part of Space Ship
line(mouseX+20,mouseY+100,mouseX+60,mouseY+70);
line(mouseX+30,mouseY+110,mouseX+60,mouseY+130);

//bullet
bulletP1X = mouseX+248;
bulletP1Y =mouseY+100; 
bulletP2X = mouseX+207;
bulletP2Y = mouseY+100;
bulletRextX = mouseX+215;
bulletRextY = mouseY+95;
bulletT1X = mouseX+240;
bulletT1Y = mouseY+100;
bulletT2X = mouseX+215;
bulletT2Y = mouseY+100;

  fill(255,0,0);
  strokeWeight(5);
  stroke(255,0,0);  
  //side tips
  point(bulletP1X,bulletP1Y);  
  point(bulletP2X,bulletP2Y);

  //bullet body
  strokeWeight(1);
  fill(255,255,255);
  rect(bulletRextX,bulletRextY,24,10);

  //TWO_PI IS FULL CIRCLE
  //PI + HALF_PI == 1.5 PI == -0.5 PI
  //TAU + HALF_PI == TWO_PI + HALF_PI == 2.5 PI == 0.5 PI

  //round ends of bullet
  arc(bulletT1X,bulletT1Y,12,12,-HALF_PI, HALF_PI);
  arc(bulletT2X,bulletT2Y,13,12,radians(90),radians(270));

}

这是我的代码的一部分，应该在 x 轴上移动项目符号，但它没有。

void keyPressed(){


background(0,0,0);
fill(255,0,0); 

while (bulletP1X != width || bulletP1X < width || bulletP2X != width || bulletP2X < width
      || bulletRextX != width || bulletRextX < width || bulletT1X != width || bulletT1X < width || bulletT2X != width || bulletT2X < width){   


  fill(255,255,255);
  stroke(0,0,0);

  bulletP1X +=25;
  bulletP2X+=25;
  bulletRextX +=25;
  bulletT1X+=25;
  bulletT2X+=25;

  fill(255,0,0);
  strokeWeight(5);
  stroke(255,0,0);  
  //side tips
  point(bulletP1X,bulletP1Y);  
  point(bulletP2X,bulletP2Y);

  //bullet body
  strokeWeight(1);
  fill(255,255,255);
  rect(bulletRextX,bulletRextY,24,10);

  //round ends of bullet
  arc(bulletT1X,bulletT1Y,12,12,-HALF_PI, HALF_PI);
  arc(bulletT2X,bulletT2Y,13,12,radians(90),radians(270));

}

if (bulletP1X == width || bulletP1X > width || bulletP2X == width || bulletP2X > width
      || bulletRextX == width || bulletRextX > width || bulletT1X == width || bulletT1X > width || bulletT2X == width || bulletT2X > width){

   fill(255,255,255);
   stroke(0,0,0);

  //bullet
  bulletP1X = mouseX+248;
  bulletP1Y =mouseY+100; 
  bulletP2X = mouseX+207;
  bulletP2Y = mouseY+100;
  bulletRextX = mouseX+215;
  bulletRextY = mouseY+95;
  bulletT1X = mouseX+240;
  bulletT1Y = mouseY+100;
  bulletT2X = mouseX+215;
  bulletT2Y = mouseY+100;           


  fill(255,0,0);
  strokeWeight(5);
  stroke(255,0,0);  
  //side tips
  point(bulletP1X,bulletP1Y);  
  point(bulletP2X,bulletP2Y);

  //bullet body
  strokeWeight(1);
  fill(255,255,255);
  rect(bulletRextX,bulletRextY,24,10);

  //round ends of bullet
  arc(bulletT1X,bulletT1Y,12,12,-HALF_PI, HALF_PI);
  arc(bulletT2X,bulletT2Y,13,12,radians(90),radians(270));

      }
}

Answer 1

我会推荐你一些读物：

http://forum.processing.org/two/discussion/8087/what-are-setup-and-draw

http://forum.processing.org/two/discussion/8085/i-display-images-in-sequence-but-i-see-only-the-last-one-why

http://forum.processing.org/two/discussion/8082/from-several-variables-to-arrays

http://forum.processing.org/two/discussion/8081/from-several-arrays-to-classes

函数keyPressed()因为它是兄弟mousePressed()、mouseClicked()等...不是"loops"如你所说，它们是回调函数，意思是它们是每次事件发生时调用一次，因此当按下 key 时，keyPressed() 中的代码将执行一次。

draw() 是一个无限循环，每秒尝试运行自身 60 次。它里面的命令是按顺序执行的（top -> bottom），每次循环结束时最终渲染结果。

这就是为什么在回调函数中绘制通常不是一个好主意。用它来设置状态或标志来驱动 draw() 中的东西。还有一个 while 循环将暂停执行，防止绘制到达循环的末尾并渲染图形...

还有一个内置变量 keyPressed，您可以在 draw() 中使用它来检查是否按下了某个键。

此外，每当你有很多 someVar1、someVar2...你应该考虑使用数组，如果你有一些数组保存相关的东西，比如 xPos[]， yPos[]、xSpeed[] 等等 classes 变得非常方便。看似很难，其实学了之后，事情就简单多了。

此外，为了将事物保持在所需范围内 (xPos)，模 % 运算符非常有帮助。

这里有一个简单的方法让"bullet"在按下任意键时移动，到达边缘后重置：

int initial_x = 50;
int x_pos = initial_x;
void setup() {  
    size(300, 300); 
    background(0);      

} 

void draw() { 
    background(0);
    if(keyPressed){
        x_pos+=3;
        if(x_pos >= width){
            x_pos = initial_x;
            }
        }  
    ellipse(x_pos, 100, 10, 10);
}

旁注，您可以考虑将所有代码包装在一个函数中（或者更好的 class），这样您就可以保持 draw() 的潮流。类似于：

void spaceShip(int x, int y){
    //code to draw ship at (x,y)
}

在平局中你会得到

spaceShip(mouseX, mouseY);

:)

使用 while 循环和 if 语句处理对象不会在 x 轴上移动

Processing objects won't move on x-axis using while loop & if statement

processing

key

move