Question

我正在使用VHDL在FPGA上创建Pong。我一直绞尽脑汁试图弄清楚如何做，以及矩形矩形碰撞的最佳解决方案是什么，我想我已经想出了最好的解决方案，尽管似乎有一个错误（如下所述）。

我接受了来自larsbutler's answer的建议，并使用此策略进行碰撞：

object.positionX + = object.velocityX

检查/回应碰撞

object.positionY + = object.velocityY

检查/回应碰撞

这个伪代码解释了我如何检查/响应冲突：

// right edge of ball in between objects left and right edge
// OR
// left edge of ball in between objects left and right edge
if((ball.right >= object.left && ball.right <= ball.right) || (ball.left >= object.left && ball.left <= object.right))
{
    xCollision = true;
}

// top edge of ball in between objects top and bottom edge
// OR
// bottom edge of ball in between objects top and bottom edge
if((ball.top >= object.top && ball.top <= object.bottom) || (ball.bottom <= object.bottom && ball.bottom >= object.top))
{
    yCollision = true;
}

// respond to collision
if xCollision and yCollision then
{
    // This code block is respective to each x or y update in order to resolve collision
}

请记住，屏幕的左上角是（0,0）。物体从它们的中心定位。这是一个图表：

Pong Diagram Setup

这是我想要回复的基本图表： (source)

Collision response diagram

问题：

此刻我正试图解决x碰撞问题。问题在于使用xPosition代码将球从球拍中取出以避免卡住。似乎if xVelocity < 0 then无法正确评估。假设球从左向右行进（xVelocity> 0）然后我们击中右侧的桨。 xVelocity将符号改为负（xVelocity <0）。问题if语句应该求值为true并递减xPosition以使其脱离paddle。这不会发生，而是跳过划桨，只是来回重复。我们添加或减去40的原因是用于测试，实际上是它在桨内的数量。

我的许多实现似乎陷入了这个陷阱xVelocity没有正确评估。如果你在if else中切换加号和减号，但是在我的脑海中没有任何逻辑意义，代码就可以工作。为什么它必须与我下面的相反？（请记住，xVelocity在此之前乘以-1。

-- respond to collision
if xCollision = '1' and yCollision = '1' then

    -- Change direction
    xVelocity <= xVelocity * (-1);
    -- Add glancing y velocity of paddle
    yVelocity <= yVelocity + (collisionObjects(i)(5)/4);

    -- If bouncing in the left direction
    if xVelocity < 0 then
        -- move outwards as much as we are inside the paddle
        -- Should be negating from xPosition as we are bouncing left and want to resolve that way
        xPosition <= xPosition - 40;
    else
        xPosition <= xPosition + 40;
    end if;
end if;

完整代码：（VHDL）

-- Ball collision is using discrete collision! 
-- not sweep collision which helps with small fast objects passing through each other


library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use ieee.std_logic_unsigned.all;

--note this line.The package is compiled to this directory by default.
--so don't forget to include this directory. 
library work;
--this line also is must.This includes the particular package into your program.
use work.my_package.all;

entity Ball is
    generic(
        numCollisionObjects: integer := 2;
        ballRadius : integer := 10;
        rgbColor : std_logic_vector(7 downto 0) := "111" & "111" & "11"
    );
    port(
        reset: in std_logic;
        clk: in std_logic;
        hCounter: in std_logic_vector(9 downto 0);
        vCounter: in std_logic_vector(9 downto 0);
        colObject: out type_collisionObject;
        collisionObjects: in type_collisionObjectArray(0 to numCollisionObjects-1);

        pixelOn: out std_logic;
        rgbPixel: out std_logic_vector(7 downto 0) := rgbColor
    );
end Ball;

architecture Behavioral of Ball is
    signal xPosition : integer := 0;
    signal yPosition : integer := 0;

    signal xVelocity : integer := 0;
    signal yVelocity : integer := 0;

    signal pixelBuffer : std_logic;
    signal RGBBuffer : std_logic_vector(7 downto 0) := rgbColor;

    signal colObjectBuffer: type_collisionObject;
begin
    pixelOn <= pixelBuffer;
    rgbPixel <= RGBBuffer;

    colObjectBuffer <= (xPosition, yPosition, ballRadius * 2, ballRadius * 2, xVelocity, yVelocity);
    colObject <= colObjectBuffer;

    animation: process(clk)
        variable update_clk_count: natural := 0;
        variable update_clk_prescaler: natural := 10000000; -- 833333; -- Slow because of debuging... 50 Mhz / clk_prescaler = desired speed
        --variable i: natural := 1;
        variable xCollision: std_logic := '0';
        variable yCollision: std_logic := '0';

        variable colObject_lastState: type_collisionObject;
    begin

        if rising_edge(clk) then
            -- While reset is high then we reset the positions
            if reset = '1' then

                xPosition <= SCREEN_RESX/2;
                yPosition <= SCREEN_RESY/2;

                xVelocity <= 3;
                yVelocity <= 0;

            else
                if update_clk_count >= update_clk_prescaler then

                    colObject_lastState := colObjectBuffer;

                    -- if we are hitting the left wall
                    if (xPosition - ballRadius + xVelocity) <= 0 then
                        RGBBuffer <= rgbColor;

                        if xVelocity < 0 then
                            xVelocity <= xVelocity * (-1);
                        end if;
                    end if;

                    -- if we are hitting the right wall
                    if (xPosition + ballRadius + xVelocity) >= 640 then
                        RGBBuffer <= rgbColor;

                        if xVelocity > 0 then
                            xVelocity <= xVelocity * (-1);
                        end if;
                    end if;

                    -- if we are hitting the top wall
                    if (yPosition - ballRadius + yVelocity) <= 0 then
                        RGBBuffer <= rgbColor;

                        if yVelocity < 0 then
                            yVelocity <= yVelocity * (-1);
                        end if;
                    end if;

                    -- if we are hitting the bottom wall
                    if (yPosition + ballRadius + yVelocity) >= 480 then
                        RGBBuffer <= rgbColor;

                        if yVelocity > 0 then
                            yVelocity <= yVelocity * (-1);
                        end if;
                    end if;

                    -- Update x position
                    xPosition <= xPosition + xVelocity;

                    -- Check for collision after x updates
                    if not(xVelocity = 0) then
                        for i in collisionObjects'range loop
                            xCollision := '0';
                            yCollision := '0';

                            -- right edge of ball in between objects left and right edge
                            -- OR
                            -- left edge of ball in between objects left and right edge
                            if (xPosition + ballRadius >= collisionObjects(i)(0) - (collisionObjects(i)(2)/2) and xPosition + ballRadius <= collisionObjects(i)(0) + (collisionObjects(i)(2)/2)) 
                                    OR (xPosition - ballRadius >= collisionObjects(i)(0) - (collisionObjects(i)(2)/2) and xPosition - ballRadius <= collisionObjects(i)(0) + (collisionObjects(i)(2)/2)) then
                                xCollision := '1';
                            end if;

                            -- top edge of ball in between objects top and bottom edge
                            -- OR
                            -- bottom edge of ball in between objects top and bottom edge
                            if (yPosition - ballRadius >= collisionObjects(i)(1) - (collisionObjects(i)(3)/2) and yPosition - ballRadius <= collisionObjects(i)(1) + (collisionObjects(i)(3)/2)) 
                                    OR (yPosition + ballRadius >= collisionObjects(i)(1) - (collisionObjects(i)(3)/2) and yPosition + ballRadius <= collisionObjects(i)(1) + (collisionObjects(i)(3)/2)) then
                                yCollision := '1';
                            end if;

                            -- respond to collision
                            if xCollision = '1' and yCollision = '1' then

                                -- Change direction
                                xVelocity <= xVelocity * (-1);
                                -- Add glancing y velocity of paddle
                                yVelocity <= yVelocity + (collisionObjects(i)(5)/4);

                                -- If bouncing in the left direction
                                if xVelocity < 0 then
                                    -- move outwards as much as we are inside the paddle
                                    -- Should be negating from xPosition as we are bouncing left and want to resolve that way
                                    xPosition <= xPosition - 40;
                                else
                                    xPosition <= xPosition + 40;
                                end if;
                            end if;

                        end loop;
                    end if;


                    -- Update y position
                    yPosition <= yPosition + yVelocity;

                    -- Check for collision after y updates
                    if not(yVelocity = 0) then
                        for i in collisionObjects'range loop
                            xCollision := '0';
                            yCollision := '0';

                            -- right edge of ball in between objects left and right edge
                            -- OR
                            -- left edge of ball in between objects left and right edge
                            if (xPosition + ballRadius >= collisionObjects(i)(0) - (collisionObjects(i)(2)/2) and xPosition + ballRadius <= collisionObjects(i)(0) + (collisionObjects(i)(2)/2)) 
                                    OR (xPosition - ballRadius >= collisionObjects(i)(0) - (collisionObjects(i)(2)/2) and xPosition - ballRadius <= collisionObjects(i)(0) + (collisionObjects(i)(2)/2)) then
                                xCollision := '1';
                            end if;

                            -- top edge of ball in between objects top and bottom edge
                            -- OR
                            -- bottom edge of ball in between objects top and bottom edge
                            if (yPosition - ballRadius >= collisionObjects(i)(1) - (collisionObjects(i)(3)/2) and yPosition - ballRadius <= collisionObjects(i)(1) + (collisionObjects(i)(3)/2)) 
                                    OR (yPosition + ballRadius >= collisionObjects(i)(1) - (collisionObjects(i)(3)/2) and yPosition + ballRadius <= collisionObjects(i)(1) + (collisionObjects(i)(3)/2)) then
                                yCollision := '1';
                            end if;

                            -- respond to collision
                            if xCollision = '1' and yCollision = '1' then

                                yVelocity <= yVelocity * (-1);

                                -- If ball is moving in same direction the paddle is
                                if (yVelocity < 0 and collisionObjects(i)(5) < 0) 
                                        OR (yVelocity > 0 and collisionObjects(i)(5) > 0) then
                                    yVelocity <= yVelocity + (collisionObjects(i)(5)/2);
                                end if;
                            end if;

                        end loop;
                    end if;

                    update_clk_count := 0;
                end if;
            end if;

            update_clk_count := update_clk_count + 1;
        end if;
    end process;



    drawing: process(hCounter, vCounter)
    begin
        -- If within pixel bounds of bar
        if hCounter >= (xPosition - ballRadius) and hCounter <= (xPosition + ballRadius) and vCounter >= (yPosition - ballRadius) and vCounter <= (yPosition + ballRadius) then
            pixelBuffer <= '1';
        else
            pixelBuffer <= '0';
        end if;
    end process;

end Behavioral;

来自my_package.vhd的相关信息：

constant SCREEN_RESX: integer := 640;
constant SCREEN_RESY: integer := 480;

-- 0: position X
-- 1: position Y
-- 2: size X 
-- 3: size Y
-- 4: velocityX
-- 5: velocityY
type type_collisionObject is array (0 to 5) of integer; 
type type_collisionObjectArray is array(natural range <>) of type_collisionObject;

更新

我的碰撞检测不是防弹，也不是让我满意，但我似乎确实发现了我的错误。我没有任何线索，但在VHDL中，信号在进程结束前不会更新其值，并将更新到最后一个语句。这意味着如果你把它变成负数然后添加到它上面，你只会得到补充。

我希望在指南和教程中更多地强调这一点，因为这花费了我很多时间。

Answer 1

我没有仔细检查你的代码的每一行，但看起来好像你已经在从伪代码到VHDL的翻译中引入了许多错误机会。即使代码转换是完全正确的，跟踪伪代码要比跟踪代码要困难得多......

假设你信任伪代码（我可以看到它的一些问题： - ）

为什么不翻译

if((ball.right >= object.left && ball.right <= ball.right) || (ball.left >= object.left && ball.left <= object.right))
{
    xCollision = true;
}

进入VHDL（纠正明显的）为

if (ball.right >= object.left and ball.right <= object.right) 
   or (ball.left >= object.left and ball.left <= object.right) then
   xCollision := true;
end if;

或只是

xCollision := (ball.right >= object.left and ball.right <= object.right) 
   or (ball.left >= object.left and ball.left <= object.right);

并适当地为ball，object（记录）和xCollision（布尔）创建数据类型？

进行下一步并将其作为函数或过程包装：

   function XCollision (ball, object : rect) return boolean is
   begin 
      return (ball.right >= object.left and ball.right <= ball.right) 
       or (ball.left >= object.left and ball.left <= object.right);
   end XCollision;

可以调用

   x_collision := false;
   for i in objects'range loop
      x_collision := x_collision or XCollision (ball, objects(i));
   end loop;

VHDL是一种高级语言，提供强大的类型模型 - 可能比编写伪代码的语言更好。以这种方式使用它。（你已经开始使用包了。）

您可以更轻松地编写，分析和调试VHDL。有关使用记录的替代方法，请创建枚举并使用它进行索引一系列价值观。

type Sides is (left, right, top, bottom); 
type obj_type is array (sides) of integer;
variable ball, object : obj_type;

在这种情况下，XCollision现在可以

   function XCollision (ball, object : rect) return boolean is
   begin 
      return (ball(right) >= object(left) and ...);
   end XCollision;

上面没有任何根本不可合成的东西。

虽然我已经看到了2010年某些函数的Synplicity对象构建 - 它在某些方面远远落后于XST - 奇怪的是它对于返回值的OUT参数的等效过程感到满意。

那些认为FPGA编程（设计硬件）与软件编码不同的人绝对是正确的 - 在极限范围内 - 但是当他们建议削弱你创造干净，易懂的代码的能力时，他们会说它做了什么，做了什么呢？说。

硬件设计的不同之处在于：

硬件可行吗？具有已知边界的FOR循环是可行的（给定足够大的FPGA） - 具有未知边界的WHILE循环生成未知数量的硬件......不可行！指针（VHDL访问类型）和“malloc”显然都是......
硬件小又快吗？给定足够的对象，上面的“for”循环将溢出FPGA或生成如此长的逻辑链，使其无法满足您的速度目标。然后，您必须将其转换为流水线设计（大型和快速）或状态机（小而快，但需要很多周期）才能实现目标。
使用适当的数据类型。如果我需要一个17位数字，我只需创建一个，并在C程序员可用的最佳可用大小（32位）上节省大量门。（显然，有一些软件语言允许这样做，但他们的用户仍然不是大多数）
并且毫无疑问是其他人，但这些IMO是最重要的。
评论;并行处理方面和信号的使用是可靠的进程间通信的最大区别：虽然以上几点在单个进程中是有效的;信号和多个过程与大多数其他编程范例有很大不同。

Answer 2

我查看了你的代码，但没有详细说明。我会建议你在实践中击中左墙或击中右球没有区别。我的意思是当它撞到左墙时，它会用减号改变方向。它与右墙相似。所以最好将两个不同的if子句与“或”结合起来。这将简化您的代码。

试试这个，希望它能奏效。

编辑：我用fpga做同样的游戏，但它运行正常。

VHDL中的矩形/盒子碰撞

问题：

完整代码：（VHDL）

更新

2 个答案: