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_Texture *brush = 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(SDL_Renderer *renderer, 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 */
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float x;
float y;
int i;
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dstRect.w = BRUSH_SIZE;
dstRect.h = BRUSH_SIZE;
/* setup x and y for the location of the first sprite */
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x = startx - BRUSH_SIZE / 2.0f;
y = starty - BRUSH_SIZE / 2.0f;
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/* 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(renderer, brush, NULL, &dstRect);
}
}
/*
loads the brush texture
*/
void
initializeTexture(SDL_Renderer *renderer)
{
SDL_Surface *bmp_surface;
bmp_surface = SDL_LoadBMP("stroke.bmp");
if (bmp_surface == NULL) {
fatalError("could not load stroke.bmp");
}
brush =
SDL_CreateTextureFromSurface(renderer, bmp_surface);
SDL_FreeSurface(bmp_surface);
if (brush == 0) {
fatalError("could not create brush texture");
}
/* additive blending -- laying strokes on top of eachother makes them brighter */
SDL_SetTextureBlendMode(brush, SDL_BLENDMODE_ADD);
/* set brush color (red) */
SDL_SetTextureColorMod(brush, 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_Window *window; /* main window */
SDL_Renderer *renderer;
int done; /* does user want to quit? */
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/* initialize SDL */
if (SDL_Init(SDL_INIT_VIDEO) < 0) {
fatalError("Could not initialize SDL");
}
/* create main window and renderer */
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window = SDL_CreateWindow(NULL, 0, 0, 320, 480, SDL_WINDOW_BORDERLESS | SDL_WINDOW_ALLOW_HIGHDPI);
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renderer = SDL_CreateRenderer(window, 0, 0);
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SDL_GetWindowSize(window, &w, &h);
SDL_RenderSetLogicalSize(renderer, w, h);
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/* load brush texture */
initializeTexture(renderer);
/* fill canvass initially with all black */
SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
SDL_RenderClear(renderer);
SDL_RenderPresent(renderer);
done = 0;
while (!done && SDL_WaitEvent(&event)) {
switch (event.type) {
case SDL_QUIT:
done = 1;
break;
case SDL_MOUSEMOTION:
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(renderer, x - dx, y - dy, dx, dy); /* draw line segment */
SDL_RenderPresent(renderer);
}
break;
}
}
/* cleanup */
SDL_DestroyTexture(brush);
SDL_Quit();
return 0;
}