Added SDL2 Experiment 11

A test of simple sprite animation. This will allow my Spacewar clone to have actual animated ships.

SDL2-Bits-And-Pieces/SDL2-Experiment-11.c

@@ -0,0 +1,330 @@
+// SDL Experiment 11, Barra Ó Catháin.
+// ===================================
+#include <SDL2/SDL.h>
+#include <SDL2/SDL_image.h>
+#include <SDL2/SDL_timer.h>
+#include <math.h>
+#include <stdbool.h>
+#include <stdint.h>
+
+typedef struct xyVector
+{
+	double xComponent;
+	double yComponent;
+} xyVector;
+
+// Calculate the vector from point A to point B:
+static inline void xyVectorBetweenPoints(long ax, long ay, long bx, long by, xyVector * vector)
+{
+	vector->xComponent = bx - ax;
+	vector->yComponent = by - ay;
+}
+
+// Normalize a vector, returning the magnitude:
+static inline double normalizeXYVector(xyVector * vector)
+{
+	double magnitude = sqrt(pow(vector->xComponent, 2) + pow(vector->yComponent, 2));
+	vector->xComponent /= magnitude;
+	vector->yComponent /= magnitude;
+	return magnitude;
+}
+
+// Get the angle between vectors:
+static inline double angleBetweenVectors(xyVector * vectorA, xyVector * vectorB)
+{
+	double dotProduct = (vectorA->xComponent * vectorB->xComponent) + (vectorA->yComponent * vectorB->yComponent);
+	double determinant = (vectorA->xComponent * vectorB->yComponent) - (vectorA->yComponent * vectorB->xComponent);
+
+	return atan2(dotProduct, determinant) / 0.01745329;
+}
+
+static inline void rotateXYVector(xyVector * vector, double degrees)
+{
+	double xComponent = vector->xComponent, yComponent = vector->yComponent;
+	vector->xComponent = (cos(degrees * 0.01745329) * xComponent) - (sin(degrees * 0.01745329) * yComponent);
+	vector->yComponent = (sin(degrees * 0.01745329) * xComponent) + (cos(degrees * 0.01745329) * yComponent);
+}
+
+// Add vector B to vector A:
+static inline void addXYVector(xyVector * vectorA, xyVector * vectorB)
+{
+	vectorA->xComponent += vectorB->xComponent;
+	vectorA->yComponent += vectorB->yComponent; 
+}
+
+// Add vector B to vector A, scaled for units per frame:
+static inline void addXYVectorDeltaScaled(xyVector * vectorA, xyVector * vectorB, double deltaTime)
+{
+	vectorA->xComponent += vectorB->xComponent * (0.001 * deltaTime) * 60;
+	vectorA->yComponent += vectorB->yComponent * (0.001 * deltaTime) * 60; 
+}
+
+// Multiply a vector by a scalar constant:
+static inline void multiplyXYVector(xyVector * vector, double scalar)
+{	
+	vector->xComponent *= scalar;
+	vector->yComponent *= scalar;
+}
+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);
+      }
+   }
+}
+
+int main(int argc, char ** argv)
+{
+	SDL_Event event;
+	int width = 0, height = 0;
+	long positionX = 0, positionY = 0;
+	uint32_t rendererFlags = SDL_RENDERER_ACCELERATED;
+	uint64_t thisFrameTime = SDL_GetPerformanceCounter(), lastFrameTime = 0;
+	double deltaTime = 0, gravityMagnitude = 0, gravityAcceleration = 0, frameAccumulator = 0;	
+	bool quit = false, rotatingClockwise = false, rotatingAnticlockwise = false, accelerating = false;
+	xyVector positionVector = {100, 100}, velocityVector = {0, 0}, gravityVector = {0, 0}, engineVector = {0.08, 0}, upVector = {0, 0.1};
+
+	// Initialize the SDL library, video, sound, and input:
+	if (SDL_Init(SDL_INIT_EVERYTHING) != 0)
+	{
+		printf("SDL Initialization Error: %s\n", SDL_GetError());
+	}
+
+	// Initialize image loading:
+	IMG_Init(IMG_INIT_PNG);
+	SDL_SetHint(SDL_HINT_RENDER_SCALE_QUALITY, "2");
+	
+	// Create a rectangle to put the ship in:
+	SDL_Rect shipRect;
+	shipRect.w = 32;
+	shipRect.h = 32;
+	
+	// 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);
+
+	// Load in all of our textures:
+	SDL_Texture * idleTexture, * acceleratingTexture, * clockwiseTexture, * anticlockwiseTexture, * currentTexture,
+	    * acceleratingTexture2;
+	
+	idleTexture = IMG_LoadTexture(renderer, "./11-Ship-Idle.png");
+	clockwiseTexture = IMG_LoadTexture(renderer, "./11-Ship-Clockwise.png");
+	acceleratingTexture = IMG_LoadTexture(renderer, "./11-Ship-Accelerating.png");
+	anticlockwiseTexture = IMG_LoadTexture(renderer, "./11-Ship-Anticlockwise.png");
+	acceleratingTexture2 = IMG_LoadTexture(renderer, "./11-Ship-Accelerating-Frame-2.png");
+
+	// Enable resizing the window:
+	SDL_SetWindowResizable(window, SDL_TRUE);
+
+	while (!quit)
+	{
+		lastFrameTime = thisFrameTime;
+		thisFrameTime = SDL_GetPerformanceCounter();
+		deltaTime = (double)(((thisFrameTime - lastFrameTime) * 1000) / (double)SDL_GetPerformanceFrequency());
+		
+		// Check if the user wants to quit:
+		while (SDL_PollEvent(&event))
+        {
+            switch (event.type)
+            {
+                case SDL_QUIT:
+				{
+					quit = true;
+					break;
+				}
+				case SDL_KEYDOWN:
+				{
+					switch (event.key.keysym.sym)
+					{
+						case SDLK_LEFT:
+						{						
+							rotatingAnticlockwise = true;
+							break;
+						}
+						case SDLK_RIGHT:
+						{
+							rotatingClockwise = true;
+							break;
+						}
+						case SDLK_UP:
+						{
+							accelerating = true;
+							break;
+						}
+						default:
+						{
+							break;
+						}
+					}
+					break;
+				}
+				case SDL_KEYUP:
+				{
+					switch (event.key.keysym.sym)
+					{
+						case SDLK_LEFT:
+						{
+							rotatingAnticlockwise = false;
+							break;
+						}
+						case SDLK_RIGHT:
+						{
+							rotatingClockwise = false;
+							break;
+						}
+						case SDLK_UP:
+						{
+							accelerating = false;
+							frameAccumulator = 0;
+							break;
+						}
+						default:
+						{
+							break;
+						}
+					}
+					break;
+				}
+				default:
+				{
+					break;
+				}
+            }
+        }
+
+        // Store the window's current width and height:
+		SDL_GetWindowSize(window, &width, &height);
+
+		// Calculate the vector between the star and ship:
+		xyVectorBetweenPoints(positionVector.xComponent, positionVector.yComponent, width/2, height/2, &gravityVector);
+
+		// Make it into a unit vector:
+		gravityMagnitude = normalizeXYVector(&gravityVector);
+
+		// Calculate the gravity between the star and ship:
+		gravityAcceleration = (gravityMagnitude >= 45) ?
+			(2500 / pow(gravityMagnitude, 2)):
+			0;
+		
+		// Scale the vector:
+		multiplyXYVector(&gravityVector, gravityAcceleration);
+		
+		// Wrap the position if the ship goes off-screen:
+		if(positionVector.xComponent > width + 15)
+		{
+			positionVector.xComponent = 0;
+			velocityVector.xComponent *= 0.6;
+		}
+		if(positionVector.yComponent > height + 15)
+		{
+			positionVector.yComponent = 0;
+			velocityVector.yComponent *= 0.6;
+		}
+		if(positionVector.xComponent < -15)
+		{
+			positionVector.xComponent = width;
+			velocityVector.xComponent *= 0.6;
+		}
+		if(positionVector.yComponent < -15)
+		{
+			positionVector.yComponent = height;
+			velocityVector.yComponent *= 0.6;
+		}
+
+		// Set the texture to idle:
+		currentTexture = idleTexture;
+		
+		// Rotate the engine vector if needed:
+		if(rotatingClockwise)
+		{
+			rotateXYVector(&engineVector, 0.1 * deltaTime);
+			currentTexture = clockwiseTexture;
+		}
+		if(rotatingAnticlockwise)
+		{
+			rotateXYVector(&engineVector, -0.1 * deltaTime);
+			currentTexture = anticlockwiseTexture;
+		}
+		
+		// Calculate the new current velocity:
+		addXYVectorDeltaScaled(&velocityVector, &gravityVector, deltaTime);
+		if(accelerating)
+		{
+			addXYVectorDeltaScaled(&velocityVector, &engineVector, deltaTime);
+			frameAccumulator += deltaTime;
+			currentTexture = acceleratingTexture;
+			if((long)frameAccumulator % 4)
+			{
+				currentTexture = acceleratingTexture2;
+			}
+		}
+		
+		// Calculate the new position:
+		addXYVectorDeltaScaled(&positionVector, &velocityVector, deltaTime);
+		
+		positionX = (long)positionVector.xComponent;
+		positionY = (long)positionVector.yComponent;
+
+		// Calculate the position of the sprite:
+		shipRect.x = positionX - 15;
+		shipRect.y = positionY - 15;
+		
+		// Set the colour to black:
+		SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
+
+		// Clear the screen, filling it with black:
+		SDL_RenderClear(renderer);
+
+		// Draw the ship:
+		SDL_RenderCopyEx(renderer, currentTexture, NULL, &shipRect, angleBetweenVectors(&engineVector, &upVector) + 90, NULL, 0);
+		
+		// Set the colour to yellow:
+		SDL_SetRenderDrawColor(renderer, 255, 255, 0, 255);
+
+		// Draw a circle in the center as the star:
+		DrawCircle(renderer, width/2, height/2, 30);
+
+		// Draw a line representing the velocity:
+		SDL_RenderDrawLine(renderer, positionX, positionY,
+						   (long)(positionVector.xComponent + velocityVector.xComponent * 15),
+						   (long)(positionVector.yComponent + velocityVector.yComponent * 15));
+
+		// Present the rendered graphics:
+		SDL_RenderPresent(renderer);
+	}
+	return 0;
+}
+// ===========================================================================================
+// Local Variables:
+// compile-command: "gcc `sdl2-config --libs --cflags` SDL2-Experiment-11.c -lSDL2_image -lm" 
+// End: