A mouse tracker in the style of a radar, to begin practice with SDL2.

SDL2-Experiment-01.c

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+// SDL Experiment 01, Barra Ó Catháin.
+// ===================================
+#include <SDL2/SDL.h>
+#include <SDL2/SDL_image.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, mouseX = 0, mouseY = 0;
+	uint32_t rendererFlags = SDL_RENDERER_ACCELERATED;
+	
+	// Initialize the SDL library, video, sound, and input:
+	if (SDL_Init(SDL_INIT_EVERYTHING) != 0)
+	{
+		printf("SDL Initialization Error: %s\n", SDL_GetError());
+	}
+
+	IMG_Init(IMG_INIT_PNG);
+	
+	// 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);
+
+	SDL_Texture * targetTexture;
+	targetTexture = IMG_LoadTexture(renderer, "./01-TGT.png");
+	SDL_Rect targetText;
+	targetText.w = 16;
+	targetText.h = 8;
+	
+	// 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;
+            }
+        }
+
+		// 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 neon green:
+		SDL_SetRenderDrawColor(renderer, 0, 255, 0, 255);
+
+		// Draw the "radar circle" as large as possible, centered in the window:
+		DrawCircle(renderer, width/2, height/2, getRadius(width, height));
+
+		// Draw 16 vertical grid lines, spaced evenly from each other and the window borders:
+		for(int verticalPosition = (height - ((height/16) * 16)) / 2;
+			verticalPosition <= height; verticalPosition += (height / 16))
+		{
+			SDL_RenderDrawLine(renderer, 0, verticalPosition, width, verticalPosition);
+		}
+
+		// Draw 16 horizontal grid lines, spaced evenly from each other and the window borders:
+		for(int horizontalPosition = (width - ((width/16) * 16)) / 2;
+			horizontalPosition <= width; horizontalPosition += (width / 16))
+		{
+			SDL_RenderDrawLine(renderer, horizontalPosition, 0, horizontalPosition, height);
+		}
+
+		// Set the colour to yellow:
+		SDL_SetRenderDrawColor(renderer, 255, 255, 0, 255);
+
+		// Store the mouse pointer's current position in the window:
+		SDL_GetMouseState(&mouseX, &mouseY);
+
+		// Draw a line from the center of the window to the mouse pointer:
+		SDL_RenderDrawLine(renderer, width/2, height/2, mouseX, mouseY);
+
+		// Draw a circle around the mouse pointer:
+		DrawCircle(renderer, mouseX, mouseY, 15);
+
+		// Set the rect at the correct position to put the TGT down:
+		targetText.x = mouseX + 20;
+		targetText.y = mouseY - 4;
+		if(mouseX < width/2)
+		{
+			targetText.x = mouseX - 36;
+		}
+		SDL_RenderCopy(renderer, targetTexture, NULL, &targetText);
+		// Present the rendered graphics:
+		SDL_RenderPresent(renderer);
+
+		// Delay enough so that we run at 144 frames:
+		SDL_Delay(1000 / 144);
+	}
+	return 0;
+}
+// ===========================================================================================
+// Local Variables:
+// compile-command: "gcc `sdl2-config --libs --cflags` SDL2-Experiment-01.c  -lSDL2_image -lm"
+// End: