1 | #include <unistd.h>
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2 | #include <stdio.h>
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3 | #include <stdlib.h>
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4 | #include <string.h>
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5 | #include <fcntl.h>
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6 | #include <linux/fb.h>
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7 | #include <sys/mman.h>
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8 |
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9 | // 'global' variables to store screen info
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10 | char *fbp = 0;
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11 | struct fb_var_screeninfo vinfo;
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12 | struct fb_fix_screeninfo finfo;
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13 |
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14 | // helper function to 'plot' a pixel in given color
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15 | //
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16 | // x, y sind Pixelkoordinaten, (0,0) ist links oben
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17 | // color ist Farbe als unsigned long: 0x00rrggbb für RGB
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18 | //
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19 | void put_pixel(long x, long y, long c)
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20 | {
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21 | unsigned long pix_offset;
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22 |
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23 | pix_offset = 3 * x + y * finfo.line_length;
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24 | *((char*)(fbp + pix_offset )) = (unsigned char)(c & 0x000000ff);
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25 | *((char*)(fbp + pix_offset+1)) = (unsigned char)((c >> 8) & 0x000000ff);
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26 | *((char*)(fbp + pix_offset+2)) = (unsigned char)((c >> 16) & 0x000000ff);
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27 | return;
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28 | }
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29 |
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30 | // helper function for drawing - no more need to go mess with the main function when just want to change what to draw...
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31 | void draw(void)
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32 | {
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33 | long x, y, c;
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34 | unsigned char r, g, b;
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35 |
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36 | for (y = 0; y < vinfo.yres; y++)
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37 | {
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38 | for (x = 0; x < vinfo.xres; x++)
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39 | {
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40 | r = 0;
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41 | g = 0;
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42 | b = 0;
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43 | // oberes Bildviertel: Balken, links schwarz,
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44 | // nach rechts überblenden zu rot
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45 | if ((y >= 0) && (y < vinfo.yres/4))
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46 | {
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47 | r = (unsigned char)((255*x)/vinfo.xres);
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48 | }
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49 | // zweites Bildviertel: Balken, links schwarz,
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50 | // nach rechts überblenden zu grün
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51 | if ((y >= vinfo.yres/4) && (y < vinfo.yres/2))
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52 | {
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53 | g = (unsigned char)((255*x)/vinfo.xres);
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54 | }
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55 | // drittes Bildviertel: Balken, links schwarz,
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56 | // nach rechts überblenden zu blau
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57 | if ((y >= vinfo.yres/2) && (y < vinfo.yres*3/4))
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58 | {
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59 | b = (unsigned char)((255*x)/vinfo.xres);
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60 | }
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61 | // unteres Bildviertel: Balken, links schwarz,
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62 | // nach rechts überblenden zu weiß
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63 | if ((y >= vinfo.yres*3/4) && (y <= vinfo.yres))
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64 | {
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65 | r = (unsigned char)((255*x)/vinfo.xres);
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66 | g = (unsigned char)((255*x)/vinfo.xres);
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67 | b = (unsigned char)((255*x)/vinfo.xres);
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68 | }
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69 | c = (int)(((r << 16) & 0x00ff0000) | ((g << 8) & 0x0000ff00) | (b & 0x000000ff));
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70 | put_pixel(x, y, c);
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71 | }
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72 | }
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73 | return;
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74 | }
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75 |
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76 | // application entry point
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77 | int main(int argc, char* argv[])
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78 | {
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79 | int fbfd = 0;
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80 | struct fb_var_screeninfo orig_vinfo;
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81 | long int screensize = 0;
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82 | long int x;
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83 |
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84 | fbfd = open("/dev/fb0", O_RDWR); // Open the file for reading and writing
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85 | if (!fbfd)
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86 | {
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87 | // printf("Error: cannot open framebuffer device.\n");
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88 | return(1);
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89 | }
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90 | // printf("The framebuffer device was opened successfully.\n");
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91 |
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92 | if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) // Get variable screen information
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93 | {
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94 | // printf("Error reading variable information.\n");
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95 | }
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96 | // printf("Original %dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel);
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97 |
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98 | memcpy(&orig_vinfo, &vinfo, sizeof(struct fb_var_screeninfo)); // Store for reset (copy vinfo to vinfo_orig)
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99 |
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100 | vinfo.bits_per_pixel = 24; // Change variable info
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101 | if (ioctl(fbfd, FBIOPUT_VSCREENINFO, &vinfo))
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102 | {
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103 | // printf("Error setting variable information.\n");
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104 | }
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105 |
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106 | if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) // Get fixed screen information
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107 | {
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108 | // printf("Error reading fixed information.\n");
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109 | }
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110 |
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111 | screensize = 3 * vinfo.xres * vinfo.yres; // map fb to user mem
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112 | fbp = (char*)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED, fbfd, 0);
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113 |
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114 | if ((int)fbp == -1)
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115 | {
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116 | // printf("Failed to mmap.\n");
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117 | }
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118 | else
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119 | {
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120 | // draw...
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121 | draw();
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122 | for (x = 0; x < 200000000; x++); // delay, danach Programm beenden
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123 | }
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124 |
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125 | munmap(fbp, screensize); // cleanup
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126 | if (ioctl(fbfd, FBIOPUT_VSCREENINFO, &orig_vinfo))
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127 | {
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128 | // printf("Error re-setting variable information.\n");
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129 | }
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130 | close(fbfd);
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131 |
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132 | return 0;
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133 | }
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