A simple gravity simulation inspired by "Spacewar!". I'm going to make this into a Spacewar! clone.
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@ -1,7 +1,8 @@
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// SDL Experiment 04, Barra Ó Catháin.
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// SDL Experiment 05, Barra Ó Catháin.
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// ===================================
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#include <SDL2/SDL.h>
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#include <SDL2/SDL_timer.h>
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#include <math.h>
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#include <stdbool.h>
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#include <stdint.h>
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@ -43,21 +44,15 @@ void DrawCircle(SDL_Renderer * renderer, int32_t centreX, int32_t centreY, int32
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}
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}
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// Get the largest radius for a circle that can fit in the width and height of a rectangle:
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static inline int getRadius(int width, int height)
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{
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return (width/2 < height/2) ? width/2 : height/2;
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}
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int main(int argc, char ** argv)
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{
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SDL_Event event;
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bool quit = false;
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int width = 0, height = 0;
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uint32_t rendererFlags = SDL_RENDERER_ACCELERATED;
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long positionX = 320, positionY = 320, velocityX = 0, velocityY = 0;
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bool accelLeft = false, accelRight = false, accelUp = false, accelDown = false;
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double posX = 0, posY = 0;
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long positionX = 0, positionY = 0;
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double velocityX = 20, velocityY = 0, gravityX = 0, gravityY = 0, gravityMagnitude = 0, gravityAcceleration = 0;
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// Initialize the SDL library, video, sound, and input:
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if (SDL_Init(SDL_INIT_EVERYTHING) != 0)
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@ -84,70 +79,6 @@ int main(int argc, char ** argv)
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quit = true;
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break;
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}
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// Begin accelerating in the direction that is pressed:
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case SDL_KEYDOWN:
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{
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switch (event.key.keysym.sym)
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{
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case SDLK_LEFT:
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{
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accelLeft = true;
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break;
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}
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case SDLK_RIGHT:
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{
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accelRight = true;
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break;
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}
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case SDLK_UP:
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{
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accelUp = true;
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break;
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}
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case SDLK_DOWN:
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{
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accelDown = true;
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break;
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}
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default:
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{
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break;
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}
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}
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break;
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}
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// Stop accelerating in the direction that is released:
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case SDL_KEYUP:
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{
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switch (event.key.keysym.sym)
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{
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case SDLK_LEFT:
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{
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accelLeft = false;
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break;
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}
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case SDLK_RIGHT:
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{
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accelRight = false;
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break;
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}
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case SDLK_UP:
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{
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accelUp = false;
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break;
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}
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case SDLK_DOWN:
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{
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accelDown = false;
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break;
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}
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default:
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{
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break;
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}
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}
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break;
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}
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default:
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{
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break;
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@ -155,106 +86,96 @@ int main(int argc, char ** argv)
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}
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}
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// Accelerate:
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if(accelLeft)
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{
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velocityX -= 2;
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}
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if(accelRight)
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{
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velocityX += 2;
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}
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if(accelUp)
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{
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velocityY -= 2;
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}
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if(accelDown)
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{
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velocityY += 2;
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}
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// Limit velocity:
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if(velocityX > 10)
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{
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velocityX = 10;
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}
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if(velocityX < -10)
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{
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velocityX = -10;
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}
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// Deccelerate:
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if(velocityX != 0)
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{
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velocityX = (velocityX < 0) ? velocityX + 1 : velocityX - 1;
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}
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if(positionY < 640)
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{
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velocityY += 1;
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}
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if(positionY >= 640 && velocityY !=0 && !accelUp)
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{
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velocityY *= -1;
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velocityY += 1;
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}
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// Move the position:
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if(velocityX != 0)
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{
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positionX += velocityX;
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if(positionX < 0)
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{
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positionX = 640;
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}
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if(positionX > 640)
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{
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positionX = 0;
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}
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}
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if(velocityY != 0)
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{
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positionY += velocityY;
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if(positionY < 0)
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{
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positionY = 0;
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}
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if(positionY > 640)
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{
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positionY = 640;
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}
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}
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// Store the window's current width and height:
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// Store the window's current width and height:
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SDL_GetWindowSize(window, &width, &height);
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// Calculate the gravity vector:
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// Calculate the vector between the star and ship:
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gravityX = (width/2 - posX);
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gravityY = (height/2 - posY);
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// Make it into a unit vector:
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gravityMagnitude = sqrt(pow(gravityX, 2) + pow(gravityY, 2));
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gravityX /= gravityMagnitude;
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gravityY /= gravityMagnitude;
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// Calculate the gravity between them and scale the vector:
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if(gravityMagnitude > 15)
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{
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gravityAcceleration = 2 * (2500 / pow(gravityMagnitude, 2));
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gravityX *= gravityAcceleration;
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gravityY *= gravityAcceleration;
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}
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else
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{
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gravityAcceleration = 0.02 * (2500 / pow(gravityMagnitude, 2));
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gravityX *= gravityAcceleration;
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gravityY *= gravityAcceleration;
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}
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// Wrap the position if the ship goes off-screen:
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if(posX > width + 15)
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{
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posX = 0;
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velocityX *= 0.6;
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}
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if(posY > height + 15)
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{
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posY = 0;
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velocityY *= 0.6;
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}
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if(posX < -15)
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{
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posX = width;
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velocityX *= 0.6;
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}
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if(posY < -15)
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{
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posY = height;
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velocityY *= 0.6;
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}
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// Calculate the new current velocity:
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velocityX += gravityX;
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velocityY += gravityY;
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// Calculate the new position:
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posX += velocityX;
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posY += velocityY;
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positionX = (long)posX;
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positionY = (long)posY;
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// Set the colour to black:
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SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
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// Clear the screen, filling it with black:
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SDL_RenderClear(renderer);
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// Set the colour to green:
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SDL_SetRenderDrawColor(renderer, 0, 255, 0, 255);
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// Draw a circle "ship" around the current position:
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DrawCircle(renderer, positionX, positionY, 15);
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// Set the colour to yellow:
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SDL_SetRenderDrawColor(renderer, 255, 255, 0, 255);
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// Draw a circle around the position pointer:
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DrawCircle(renderer, positionX, positionY, 15);
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// Draw a circle in the center as the star:
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DrawCircle(renderer, width/2, height/2, 30);
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// Draw a line representing the velocity:
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SDL_RenderDrawLine(renderer, positionX, positionY, (long)((posX + velocityX * 3)), (long)((posY + velocityY * 3)));
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// Present the rendered graphics:
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SDL_RenderPresent(renderer);
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// Delay enough so that we run at 144 frames:
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// Delay enough so that we run at 60 frames:
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SDL_Delay(1000 / 60);
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}
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return 0;
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}
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// ===========================================================================================
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// Local Variables:
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// compile-command: "gcc `sdl2-config --libs --cflags` SDL2-Experiment-04.c -lm"
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// compile-command: "gcc `sdl2-config --libs --cflags` SDL2-Experiment-05.c -lm"
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// End:
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