Touch input demo (multitouch)

XCodeiPhoneOS/Demos/src/touch.c

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+/*
+ *	touch.c
+ *	written by Holmes Futrell
+ *	use however you want
+ */
+
+#include "SDL.h"
+#include "math.h"
+#include "common.h"
+
+#define BRUSH_SIZE 32			/* width and height of the brush */
+#define PIXELS_PER_ITERATION 5  /* number of pixels between brush blots when forming a line */ 
+
+static SDL_TextureID brushID=0; /* texture for the brush */
+
+/*
+	draws a line from (startx, starty) to (startx + dx, starty + dy)
+	this is accomplished by drawing several blots spaced PIXELS_PER_ITERATION apart
+*/
+void drawLine(float startx, float starty, float dx, float dy) {
+
+	float distance = sqrt(dx*dx+dy*dy);						/* length of line segment (pythagoras) */
+	int iterations = distance / PIXELS_PER_ITERATION + 1;	/* number of brush sprites to draw for the line */
+	float dx_prime = dx / iterations;						/* x-shift per iteration */
+	float dy_prime = dy / iterations;						/* y-shift per iteration */
+	SDL_Rect dstRect;										/* rect to draw brush sprite into */
+
+	dstRect.w = BRUSH_SIZE;
+	dstRect.h = BRUSH_SIZE;
+
+	/* setup x and y for the location of the first sprite */
+	float x = startx - BRUSH_SIZE / 2.0f;
+	float y = starty - BRUSH_SIZE / 2.0f;		
+
+	int i;
+	/* draw a series of blots to form the line */
+	for (i=0; i<iterations; i++) {
+		dstRect.x = x;
+		dstRect.y = y;
+		/* shift x and y for next sprite location */
+		x += dx_prime;
+		y += dy_prime;
+		/* draw brush blot */
+		SDL_RenderCopy(brushID, NULL, &dstRect);
+	}
+}
+
+/*
+	loads the brush texture
+*/
+void initializeTexture() {
+	SDL_Surface *bmp_surface;
+	bmp_surface = SDL_LoadBMP("stroke.bmp");
+	if (bmp_surface == NULL) {
+		fatalError("could not load stroke.bmp");
+	}
+	brushID = SDL_CreateTextureFromSurface(SDL_PIXELFORMAT_ABGR8888, bmp_surface);
+	SDL_FreeSurface(bmp_surface);
+	if (brushID == 0) {
+		fatalError("could not create brush texture");
+	}
+	/* additive blending -- laying strokes on top of eachother makes them brighter */
+	SDL_SetTextureBlendMode(brushID, SDL_TEXTUREBLENDMODE_ADD);
+	/* set brush color (red) */
+	SDL_SetTextureColorMod(brushID, 255, 100, 100);
+}
+
+int main(int argc, char *argv[]) {
+
+	int x, y, dx, dy;		/* mouse location	   */
+	Uint8 state;			/* mouse (touch) state */
+	SDL_Event event;
+	SDL_WindowID windowID;	/* main window */
+	int done;				/* does user want to quit? */
+
+	/* initialize SDL */
+	if (SDL_Init(SDL_INIT_VIDEO) < 0) {
+		fatalError("Could not initialize SDL");
+	}
+
+	/* create main window and renderer */
+	windowID = SDL_CreateWindow(NULL, 0, 0, SCREEN_WIDTH, SCREEN_HEIGHT,\
+								SDL_WINDOW_OPENGL|SDL_WINDOW_SHOWN|SDL_WINDOW_BORDERLESS);
+	SDL_CreateRenderer(windowID, 0, 0);		
+
+	/*load brush texture */
+	initializeTexture();
+
+	/* fill canvass initially with all black */
+	SDL_RenderFill(0, 0, 0, 255, NULL);
+	SDL_RenderPresent();
+
+	done = 0;
+	while (!done && SDL_WaitEvent(&event)) {
+		switch (event.type) {
+			case SDL_QUIT:
+				done = 1;
+				break;
+			case SDL_MOUSEMOTION:
+				SDL_SelectMouse(event.motion.which);  /* select 'mouse' (touch) that moved */
+				state = SDL_GetMouseState(&x, &y);	  /* get its location */
+				SDL_GetRelativeMouseState(&dx, &dy);  /* find how much the mouse moved */
+				if (state & SDL_BUTTON_LMASK) {		  /* is the mouse (touch) down? */
+					drawLine(x - dx, y - dy, dx, dy); /* draw line segment */
+					SDL_RenderPresent();
+				}
+				break;
+		}
+	}
+
+	/* cleanup */
+	SDL_DestroyTexture(brushID);
+	SDL_Quit();
+
+	return 0;
+}