PPrinciples2017/breakout/paddleAndBall.c

#ifdef _WIN32
#include <SDL.h>
#else
#include <SDL2/SDL.h>
#endif
#include "include/structs.h"
#include "include/utilityFunctions.h"

void updatePaddle(Uint32 tickrate, paddle *thePaddle, char moveX, int winWidth, int winHeight) {
  thePaddle->x += moveX * 0.5 * tickrate;
  if (thePaddle->x < 0 - (thePaddle->width / 2)) thePaddle->x = 0 - (thePaddle->width / 2);
  if (thePaddle->x > winWidth - (thePaddle->width / 2)) thePaddle->x = winWidth - (thePaddle->width / 2);
}

void updateBall(Uint32 tickrate, ball *theBall, paddle *thePaddle, int winWidth, int winHeight, brick *bricks, int brickCount, int *playerLives) {
  if (theBall->stickToPaddle == 0) {
    double ballNX = theBall->x + theBall->vX * 0.1 * tickrate; // Calculates the position of the ball's centre on the next step
    double ballNY = theBall->y + theBall->vY * 0.1 * tickrate;

    double paddleRX = thePaddle->x - (double)(winWidth / 2);   // Converts paddle X/Y to coordinates relative to the center of the window as the ball
    double paddleRY = 20 - (double)(winHeight / 2);            // (Default is absolute, offset from the top left corner of window) 

    coord paddleQ[4] = {
      { .x = paddleRX,.y = paddleRY }, // Sets up a quad (coord array) to pass to vertexWithinQuad function later
    { .x = paddleRX,.y = paddleRY - thePaddle->height },
    { .x = paddleRX + thePaddle->width,.y = paddleRY - thePaddle->height },
    { .x = paddleRX + thePaddle->width,.y = paddleRY },
    };

    // Collision with paddle
    // (Testing each vertex of ball against paddle quad)

    char colliding = 0;
    int mults[4] = { -1,-1,1,1 };

    for (int i = 0, j = 3; i < 4; i++, j++) {
      coord ballN = { .x = ballNX + (theBall->radius*mults[i % 4]),.y = ballNY + (theBall->radius*mults[j % 4]) }; // Constructs pairs of coordinates referring to each vertex of the ball
      if (vertexWithinQuad(ballN, paddleQ)) colliding = 1;
    }

    if (colliding) {
      if (theBall->isColliding == 0) {

        theBall->isColliding = 1; // This keeps track of any current attepmts to 'solve' collision
                                  // Without this flag, if the ball ends up within another object and moving slow enough that on the next frame it has not escaped the object,
                                  // it will repeatedly have its velocity multiplied by -1 and get stuck, effectively moving only along one axis. With this flag,
                                  // the game will ignore subsequent collisions, until it is no longer colliding. Note this does not solve the same problem where two objects
                                  // are very close to each other and on exiting one object it enters another, in which case the ball will move through the other objects

        if (theBall->x + theBall->radius < paddleRX) { // Left side collision
          theBall->vX *= -1.0;
        }
        else if (theBall->x - theBall->radius > paddleRX + thePaddle->width) { // Right side collision
          theBall->vX *= -1.0;
        }
        else { // Top or bottom collision
          theBall->vY *= -1.0;
          theBall->vX = ((ballNX - paddleRX - (double)(thePaddle->width / 2)) / ((double)thePaddle->width / 2))*theBall->initVX; // Sets X velocity to be proportional to the relative position of the ball and the paddle on collision
        }
      }
      else {
        // Already solving a collision
      }
    }
    else {
      theBall->isColliding = 0;
    }

    // Collision with bricks
    // (Testing each vertex of ball against every brick)

    for (int i = 0; i < brickCount; i++) {
      colliding = 0;

      if (bricks[i].destroyed == 0) {
        coord brick[4] = {
          { .x = bricks[i].x - (winWidth / 2),.y = bricks[i].y },
        { .x = bricks[i].x - (winWidth / 2),.y = bricks[i].y - bricks[i].height },
        { .x = bricks[i].x - (winWidth / 2) + bricks[i].width,.y = bricks[i].y - bricks[i].height },
        { .x = bricks[i].x - (winWidth / 2) + bricks[i].width,.y = bricks[i].y },
        };

        for (int j = 0, k = 3; j < 4; j++, k++) {
          coord ballN = { .x = ballNX + (theBall->radius*mults[j % 4]),.y = ballNY + (theBall->radius*mults[k % 4]) };
          if (vertexWithinQuad(ballN, brick)) colliding = 1;
        }

        if (colliding) {
          if (theBall->x + theBall->radius < bricks[i].x - (winWidth / 2)) { // Left side collision
            theBall->vX *= -1.0;
          }
          else if (theBall->x - theBall->radius > bricks[i].x - (winWidth / 2) + bricks[i].width) { // Right side collision
            theBall->vX *= -1.0;
          }
          else {
            theBall->vY *= -1.0;
          }
          bricks[i].destroyed = 1;
          break;
        }
      }
    }

    // Collision with window boundaries

    if (ballNX > winWidth / 2 || ballNX < (-1.0*winWidth / 2)) { // Collision with walls
      theBall->vX *= -1.0;
    }
    if (ballNY > winHeight / 2) { // Collision with ceiling
      theBall->vY *= -1.0;
    }
    if (ballNY < (-1.0*winHeight / 2)) { // Collision with floor
      theBall->x = 0;
      theBall->y = 0;
      theBall->vX = theBall->initVX;
      theBall->vY = theBall->initVY;
      *playerLives -= 1;
    }

    // Update the ball's position

    theBall->x += theBall->vX * 0.1 * tickrate;
    theBall->y += theBall->vY * 0.1 * tickrate;
  }
  else {
    theBall->x = thePaddle->x - (double)(winWidth / 2) + (thePaddle->width) / 2;
    theBall->y = 26 - (double)(winHeight / 2);
  }
}