2023-02-01 16:13:31 +00:00
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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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void DrawCircle(SDL_Renderer * renderer, int32_t centreX, int32_t centreY, int32_t radius)
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{
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const int32_t diameter = (radius * 2);
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int32_t x = (radius - 1);
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int32_t y = 0;
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int32_t tx = 1;
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int32_t ty = 1;
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int32_t error = (tx - diameter);
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while (x >= y)
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{
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// Each of the following renders an octant of the circle
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SDL_RenderDrawPoint(renderer, centreX + x, centreY - y);
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SDL_RenderDrawPoint(renderer, centreX + x, centreY + y);
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SDL_RenderDrawPoint(renderer, centreX - x, centreY - y);
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SDL_RenderDrawPoint(renderer, centreX - x, centreY + y);
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SDL_RenderDrawPoint(renderer, centreX + y, centreY - x);
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SDL_RenderDrawPoint(renderer, centreX + y, centreY + x);
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SDL_RenderDrawPoint(renderer, centreX - y, centreY - x);
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SDL_RenderDrawPoint(renderer, centreX - y, centreY + x);
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if (error <= 0)
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{
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++y;
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error += ty;
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ty += 2;
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}
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if (error > 0)
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{
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--x;
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tx += 2;
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error += (tx - diameter);
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}
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}
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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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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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{
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printf("SDL Initialization Error: %s\n", SDL_GetError());
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}
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// Create an SDL window and rendering context in that window:
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SDL_Window * window = SDL_CreateWindow("SDL_TEST", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 640, 640, 0);
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SDL_Renderer * renderer = SDL_CreateRenderer(window, -1, rendererFlags);
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// Enable resizing the window:
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SDL_SetWindowResizable(window, SDL_TRUE);
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while (!quit)
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{
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// Check if the user wants to quit:
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while (SDL_PollEvent(&event))
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{
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switch (event.type)
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{
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case SDL_QUIT:
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{
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quit = 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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}
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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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2023-02-02 14:59:06 +00:00
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if(gravityMagnitude > 15)
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2023-02-01 16:13:31 +00:00
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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 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 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-05.c -lm"
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// End:
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