Added SDL2 Experiment 4

Adapted the previous acceleration example to do basic "physics." Gravity, and bouncing.
More of a simulation experiment than an SDL one.y

SDL2-Bits-And-Pieces/SDL2-Experiment-04.c

@@ -0,0 +1,265 @@
+// SDL Experiment 04, Barra Ó Catháin.
+// ===================================
+#include <SDL2/SDL.h>
+#include <SDL2/SDL_timer.h>
+#include <stdbool.h>
+#include <stdint.h>
+
+void DrawCircle(SDL_Renderer * renderer, int32_t centreX, int32_t centreY, int32_t radius)
+{
+   const int32_t diameter = (radius * 2);
+
+   int32_t x = (radius - 1);
+   int32_t y = 0;
+   int32_t tx = 1;
+   int32_t ty = 1;
+   int32_t error = (tx - diameter);
+
+   while (x >= y)
+   {
+	 //  Each of the following renders an octant of the circle
+      SDL_RenderDrawPoint(renderer, centreX + x, centreY - y);
+      SDL_RenderDrawPoint(renderer, centreX + x, centreY + y);
+      SDL_RenderDrawPoint(renderer, centreX - x, centreY - y);
+      SDL_RenderDrawPoint(renderer, centreX - x, centreY + y);
+      SDL_RenderDrawPoint(renderer, centreX + y, centreY - x);
+      SDL_RenderDrawPoint(renderer, centreX + y, centreY + x);
+      SDL_RenderDrawPoint(renderer, centreX - y, centreY - x);
+      SDL_RenderDrawPoint(renderer, centreX - y, centreY + x);
+
+      if (error <= 0)
+      {
+         ++y;
+         error += ty;
+         ty += 2;
+      }
+
+      if (error > 0)
+      {
+         --x;
+         tx += 2;
+         error += (tx - diameter);
+      }
+   }
+}
+
+// Get the largest radius for a circle that can fit in the width and height of a rectangle:
+static inline int getRadius(int width, int height)
+{
+	return (width/2 < height/2) ? width/2 : height/2;
+}
+
+
+int main(int argc, char ** argv)
+{
+	SDL_Event event;
+	bool quit = false;
+	int width = 0, height = 0;
+	uint32_t rendererFlags = SDL_RENDERER_ACCELERATED;
+	long positionX = 320, positionY = 320, velocityX = 0, velocityY = 0;
+	bool accelLeft = false, accelRight = false, accelUp = false, accelDown = false;
+
+	// Initialize the SDL library, video, sound, and input:
+	if (SDL_Init(SDL_INIT_EVERYTHING) != 0)
+	{
+		printf("SDL Initialization Error: %s\n", SDL_GetError());
+	}
+
+	if (SDL_Init(SDL_INIT_EVERYTHING) != 0)
+	{
+		printf("SDL Initialization Error: %s\n", SDL_GetError());
+	}
+	
+	// Create an SDL window and rendering context in that window:
+	SDL_Window * window = SDL_CreateWindow("SDL_TEST", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 640, 640, 0);
+	SDL_Renderer * renderer = SDL_CreateRenderer(window, -1, rendererFlags);
+	
+	// Enable resizing the window:
+	SDL_SetWindowResizable(window, SDL_TRUE);
+
+	while (!quit)
+	{
+		// Check if the user wants to quit:
+		while (SDL_PollEvent(&event))
+        {
+            switch (event.type)
+            {
+                case SDL_QUIT:
+				{
+					quit = true;
+					break;
+				}
+				// Begin accelerating in the direction that is pressed:
+				case SDL_KEYDOWN:
+				{
+					switch (event.key.keysym.sym)
+					{
+						case SDLK_LEFT:
+						{
+							accelLeft = true;
+							break;
+						}
+						case SDLK_RIGHT:
+						{
+							accelRight = true;
+							break;
+						}
+						case SDLK_UP:
+						{
+							accelUp = true;
+							break;
+						}
+						case SDLK_DOWN:
+						{
+							accelDown = true;
+							break;
+						}					  
+						default:
+						{
+							break;
+						}
+					}
+					break;
+				}
+				// Stop accelerating in the direction that is released:
+				case SDL_KEYUP:
+				{
+					switch (event.key.keysym.sym)
+					{
+						case SDLK_LEFT:
+						{
+							accelLeft = false;
+							break;
+						}
+						case SDLK_RIGHT:
+						{
+							accelRight = false;
+							break;
+						}
+						case SDLK_UP:
+						{
+							accelUp = false;
+							break;
+						}
+						case SDLK_DOWN:
+						{
+							accelDown = false;
+							break;
+						}
+						default:
+						{
+							break;
+						}
+					}
+					break;
+				}
+				default:
+				{
+					break;
+				}
+            }
+        }
+
+		// Accelerate:
+		if(accelLeft)
+		{
+			velocityX -= 2;
+		}
+
+		if(accelRight)
+		{
+			velocityX += 2;
+		}
+
+		if(accelUp)
+		{
+			velocityY -= 2;
+		}
+
+		if(accelDown)
+		{
+			velocityY += 2;
+		}
+
+		// Limit velocity:
+		if(velocityX > 10)
+		{
+			velocityX = 10;
+		}
+
+		if(velocityX < -10)
+		{
+			velocityX = -10;
+		}
+
+		
+		// Deccelerate:
+		if(velocityX != 0)
+		{
+			velocityX = (velocityX < 0) ? velocityX + 1 : velocityX - 1;
+		}
+
+		if(positionY < 640)
+		{
+			velocityY += 1;
+		}
+		if(positionY >= 640 && velocityY !=0 && !accelUp)
+		{
+			velocityY *= -1;
+			velocityY += 1;
+		}
+
+		
+		// Move the position:
+		if(velocityX != 0)
+		{
+			positionX += velocityX;
+			if(positionX < 0)
+			{
+				positionX = 640;
+			}
+			if(positionX > 640)
+			{
+				positionX = 0;
+			}
+		}
+		if(velocityY != 0)
+		{
+			positionY += velocityY;
+			if(positionY < 0)
+			{
+				positionY = 0;
+			}
+			if(positionY > 640)
+			{
+				positionY = 640;
+			}
+		}
+		
+		// Store the window's current width and height:
+		SDL_GetWindowSize(window, &width, &height);
+
+		// Set the colour to black:
+		SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
+
+		// Clear the screen, filling it with black:
+		SDL_RenderClear(renderer);
+
+		// Set the colour to yellow:
+		SDL_SetRenderDrawColor(renderer, 255, 255, 0, 255);
+		
+		// Draw a circle around the position pointer:
+		DrawCircle(renderer, positionX, positionY, 15);
+
+		// Present the rendered graphics:
+		SDL_RenderPresent(renderer);
+
+		// Delay enough so that we run at 144 frames:
+		SDL_Delay(1000 / 60);
+	}
+	return 0;
+}
+// ===========================================================================================
+// Local Variables:
+// compile-command: "gcc `sdl2-config --libs --cflags` SDL2-Experiment-04.c  -lm"
+// End: