Atlas - touch.c
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[FILE BEGIN]
1/*
2 *  touch.c
3 *  written by Holmes Futrell
4 *  use however you want
5 */
6
7#include "SDL.h"
8#include <math.h>
9#include "common.h"
10
11#define BRUSH_SIZE 32           /* width and height of the brush */
12#define PIXELS_PER_ITERATION 5  /* number of pixels between brush blots when forming a line */
13
14static SDL_Texture *brush = 0;       /* texture for the brush */
15
16/*
17    draws a line from (startx, starty) to (startx + dx, starty + dy)
18    this is accomplished by drawing several blots spaced PIXELS_PER_ITERATION apart
19*/
20void
21drawLine(SDL_Renderer *renderer, float startx, float starty, float dx, float dy)
22{
23
24    float distance = sqrt(dx * dx + dy * dy);   /* length of line segment (pythagoras) */
25    int iterations = distance / PIXELS_PER_ITERATION + 1;       /* number of brush sprites to draw for the line */
26    float dx_prime = dx / iterations;   /* x-shift per iteration */
27    float dy_prime = dy / iterations;   /* y-shift per iteration */
28    SDL_Rect dstRect;           /* rect to draw brush sprite into */
29    float x;
30    float y;
31    int i;
32
33    dstRect.w = BRUSH_SIZE;
34    dstRect.h = BRUSH_SIZE;
35
36    /* setup x and y for the location of the first sprite */
37    x = startx - BRUSH_SIZE / 2.0f;
38    y = starty - BRUSH_SIZE / 2.0f;
39
40    /* draw a series of blots to form the line */
41    for (i = 0; i < iterations; i++) {
42        dstRect.x = x;
43        dstRect.y = y;
44        /* shift x and y for next sprite location */
45        x += dx_prime;
46        y += dy_prime;
47        /* draw brush blot */
48        SDL_RenderCopy(renderer, brush, NULL, &dstRect);
49    }
50}
51
52/*
53    loads the brush texture
54*/
55void
56initializeTexture(SDL_Renderer *renderer)
57{
58    SDL_Surface *bmp_surface;
59    bmp_surface = SDL_LoadBMP("stroke.bmp");
60    if (bmp_surface == NULL) {
61        fatalError("could not load stroke.bmp");
62    }
63    brush =
64        SDL_CreateTextureFromSurface(renderer, bmp_surface);
65    SDL_FreeSurface(bmp_surface);
66    if (brush == 0) {
67        fatalError("could not create brush texture");
68    }
69    /* additive blending -- laying strokes on top of eachother makes them brighter */
70    SDL_SetTextureBlendMode(brush, SDL_BLENDMODE_ADD);
71    /* set brush color (red) */
72    SDL_SetTextureColorMod(brush, 255, 100, 100);
73}
74
75int
76main(int argc, char *argv[])
77{
78
79    int x, y, dx, dy;           /* mouse location          */
80    Uint8 state;                /* mouse (touch) state */
81    SDL_Event event;
82    SDL_Window *window;         /* main window */
83    SDL_Renderer *renderer;
84    int done;                   /* does user want to quit? */
85    int w, h;
86
87    /* initialize SDL */
88    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
89        fatalError("Could not initialize SDL");
90    }
91
92    /* create main window and renderer */
93    window = SDL_CreateWindow(NULL, 0, 0, 320, 480, SDL_WINDOW_BORDERLESS | SDL_WINDOW_ALLOW_HIGHDPI);
94    renderer = SDL_CreateRenderer(window, 0, 0);
95
96    SDL_GetWindowSize(window, &w, &h);
97    SDL_RenderSetLogicalSize(renderer, w, h);
98
99    /* load brush texture */
100    initializeTexture(renderer);
101
102    /* fill canvass initially with all black */
103    SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
104    SDL_RenderClear(renderer);
105    SDL_RenderPresent(renderer);
106
107    done = 0;
108    while (!done && SDL_WaitEvent(&event)) {
109        switch (event.type) {
110        case SDL_QUIT:
111            done = 1;
112            break;
113        case SDL_MOUSEMOTION:
114            state = SDL_GetMouseState(&x, &y);  /* get its location */
115            SDL_GetRelativeMouseState(&dx, &dy);        /* find how much the mouse moved */
116            if (state & SDL_BUTTON_LMASK) {     /* is the mouse (touch) down? */
117                drawLine(renderer, x - dx, y - dy, dx, dy);       /* draw line segment */
118                SDL_RenderPresent(renderer);
119            }
120            break;
121        }
122    }
123
124    /* cleanup */
125    SDL_DestroyTexture(brush);
126    SDL_Quit();
127
128    return 0;
129}
130
[FILE END]
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