1 | #ifndef BMP_H
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2 | #define BMP_H
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3 |
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4 | #include <stdint.h>
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5 |
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6 | typedef struct
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7 | {
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8 | char bfType[2]; // 19778 must always be set to 'BM' to declare that this is a .bmp-file.
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9 | uint32_t bfSize; // the size of the file in bytes.
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10 | uint16_t bfReserved1; // must always be set to zero.
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11 | uint16_t bfReserved2; // must always be set to zero.
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12 | uint32_t bfOffBits; // 1078 offset from the beginning of the file to the bitmap data.
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13 | } __attribute__ ((__packed__)) BMPFileHeader;
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14 |
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15 | typedef struct
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16 | {
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17 | uint32_t biSize; // 40 size of the BITMAPINFOHEADER structure, in bytes.
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18 | uint32_t biWidth; // width of the image, in pixels.
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19 | uint32_t biHeight; // height of the image, in pixels.
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20 | uint16_t biPlanes; // 1 planes of the target device, must be set to zero.
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21 | uint16_t biBitCount; // 8 bits per pixel.
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22 | uint32_t biCompression; // 0 the type of compression, usually set to zero (no compression).
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23 | uint32_t biSizeImage; // 0 the size of the image data, in bytes. If there is no compression, it is valid to set this member to zero.
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24 | uint32_t biXPelsPerMeter; // 0 usually set to zero.
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25 | uint32_t biYPelsPerMeter; // 0 usually set to zero.
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26 | uint32_t biClrUsed; // 0 number of colors in the bitmap, if zero, the number of colors is calculated using biBitCount
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27 | uint32_t biClrImportant; // 0 number of color that are 'important' for the bitmap, if zero, all colors are important.
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28 | } __attribute__ ((__packed__)) BMPInfoHeader;
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29 |
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30 | typedef struct
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31 | {
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32 | uint8_t blue;
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33 | uint8_t green;
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34 | uint8_t red;
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35 | uint8_t Reserved;
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36 | } __attribute__ ((__packed__)) RGBQUAD;
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37 |
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38 | typedef struct
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39 | {
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40 | BMPFileHeader bmfh;
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41 | BMPInfoHeader bmih;
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42 | RGBQUAD *colors;
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43 | uint8_t *data;
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44 | int rowlen;
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45 | } BMP;
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46 |
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47 | #endif /* BMP_H */
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48 |
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49 | /*
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50 |
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51 | The .bmp file format
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52 |
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53 | Introduction:
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54 | The .bmp file format (sometimes also saved as .dib) is the standard
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55 | for a Windows 3.0 or later DIB (device independent bitmap) file. It may
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56 | use compression (though I never came across a compressed .bmp-file)
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57 | and is (by itself) not capable of storing animation. However, you can
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58 | animate a bitmap using different methods but you have to write the
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59 | code which performs the animation. There are different ways to
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60 | compress a .bmp-file, but I won't explain them here because they are
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61 | so rarely used. The image data itself can either contain pointers to
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62 | entries in a color table or literal RGB values (this is explained
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63 | later).
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64 |
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65 | Basic structure:
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66 | A .bmp file contains of the following data structures:
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67 |
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68 | BITMAPFILEHEADER bmfh;
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69 | BITMAPINFOHEADER bmih;
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70 | RGBQUAD aColors[];
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71 | BYTE aBitmapBits[];
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72 |
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73 | bmfh contains some information about the bitmap file (about the file,
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74 | not about the bitmap itself). bmih contains information about the
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75 | bitmap such as size, colors,... The aColors array contains a color
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76 | table. The rest is the image data, which format is specified by the
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77 | bmih structure.
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78 |
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79 | Exact structure:
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80 | The following tables give exact information about the data structures
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81 | and also contain the settings for a bitmap with the following
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82 | dimensions: size 100x100, 256 colors, no compression. The start-value
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83 | is the position of the byte in the file at which the explained data
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84 | element of the structure starts, the size-value contains the nuber of
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85 | bytes used by this data element, the name-value is the name assigned
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86 | to this data element by the Microsoft API documentation. Stdvalue
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87 | stands for standard value. There actually is no such a thing as a
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88 | standard value but this is the value Paint assigns to the data element
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89 | if using the bitmap dimensions specified above (100x100x256). The
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90 | meaning-column gives a short explanation of the purpose of this data
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91 | element.
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92 |
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93 | The BITMAPFILEHEADER:
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94 | start size name stdvalue purpose
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95 | 1 2 bfType 19778 must always be set to 'BM' to declare that this is a .bmp-file.
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96 | 3 4 bfSize ?? specifies the size of the file in bytes.
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97 | 7 2 bfReserved1 0 must always be set to zero.
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98 | 9 2 bfReserved2 0 must always be set to zero.
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99 | 11 4 bfOffBits 1078 specifies the offset from the beginning of the file to the bitmap data.
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100 |
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101 | The BITMAPINFOHEADER:
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102 | start size name stdvalue purpose
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103 | 15 4 biSize 40 specifies the size of the BITMAPINFOHEADER structure, in bytes.
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104 | 19 4 biWidth 100 specifies the width of the image, in pixels.
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105 | 23 4 biHeight 100 specifies the height of the image, in pixels.
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106 | 27 2 biPlanes 1 specifies the number of planes of the target device, must be set to zero.
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107 | 29 2 biBitCount 8 specifies the number of bits per pixel.
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108 | 31 4 biCompression 0 Specifies the type of compression, usually set to zero (no compression).
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109 | 35 4 biSizeImage 0 specifies the size of the image data, in bytes. If there is no compression, it is valid to set this member to zero.
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110 | 39 4 biXPelsPerMeter 0 specifies the the horizontal pixels per meter on the designated targer device, usually set to zero.
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111 | 43 4 biYPelsPerMeter 0 specifies the the vertical pixels per meter on the designated targer device, usually set to zero.
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112 | 47 4 biClrUsed 0 specifies the number of colors used in the bitmap, if set to zero the number of colors is calculated using the biBitCount member.
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113 | 51 4 biClrImportant 0 specifies the number of color that are 'important' for the bitmap, if set to zero, all colors are important.
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114 |
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115 | Note that biBitCount actually specifies the color resolution of the
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116 | bitmap. The possible values are: 1 (black/white); 4 (16 colors); 8
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117 | (256 colors); 24 (16.7 million colors). The biBitCount data element
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118 | also decides if there is a color table in the file and how it looks
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119 | like. In 1-bit mode the color table has to contain 2 entries (usually
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120 | white and black). If a bit in the image data is clear, it points to
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121 | the first palette entry. If the bit is set, it points to the
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122 | second.
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123 |
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124 | In 4-bit mode the color table must contain 16 colors. Every
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125 | byte in the image data represents two pixels. The byte is split into
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126 | the higher 4 bits and the lower 4 bits and each value of them points
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127 | to a palette entry. There are also standard colors for 16 colors mode
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128 | (16 out of Windows 20 reserved colors (without the entries 8, 9, 246,
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129 | 247)). Note that you do not need to use this standard colors if the
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130 | bitmap is to be displayed on a screen which support 256 colors or
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131 | more, however (nearly) every 4-bit image uses this standard colors.
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132 |
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133 | In 8-bit mode every byte represents a pixel. The value points to an entry
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134 | in the color table which contains 256 entries (for details see
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135 | Palettes in Windows.
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136 |
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137 | In 24-bit mode three bytes represent one
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138 | pixel. The first byte represents the red part, the second the green
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139 | and the third the blue part. There is no need for a palette because
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140 | every pixel contains a literal RGB-value, so the palette is omitted.
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141 |
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142 |
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143 | The RGBQUAD array:
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144 | The following table shows a single RGBQUAD structure:
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145 | start size name stdvalue purpose
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146 | 1 1 rgbBlue - specifies the blue part of the color.
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147 | 2 1 rgbGreen - specifies the green part of the color.
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148 | 3 1 rgbRed - specifies the red part of the color.
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149 | 4 1 rgbReserved - must always be set to zero.
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150 |
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151 | Note that the term palette does not refer to a RGBQUAD array, which is
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152 | called color table instead. Also note that, in a color table
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153 | (RGBQUAD), the specification for a color starts with the blue byte. In
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154 | a palette a color always starts with the red byte. There is no simple
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155 | way to map the whole color table into a LOGPALETTE structure, which
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156 | you will need to display the bitmap. You will have to write a function
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157 | that copies byte after byte.
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158 |
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159 |
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160 | The pixel data:
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161 | It depens on the BITMAPINFOHEADER structure how the pixel data is to
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162 | be interpreted (see above).
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163 | It is important to know that the rows of a DIB are stored upside
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164 | down. That means that the uppest row which appears on the screen
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165 | actually is the lowest row stored in the bitmap, a short example:
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166 |
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167 |
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168 |
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169 | pixels displayed on the screen pixels stored in .bmp-file
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170 |
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171 | You do not need to turn around the rows manually. The API functions
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172 | which also display the bitmap will do that for you automatically.
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173 |
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174 | Another important thing is that the number of bytes in one row must
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175 | always be adjusted to fit into the border of a multiple of four. You
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176 | simply append zero bytes until the number of bytes in a row reaches a
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177 | multiple of four, an example:
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178 |
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179 |
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180 | 6 bytes that represent a row in the bitmap: A0 37 F2 8B 31 C4
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181 | must be saved as: A0 37 F2 8B 31 C4 00 00
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182 |
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183 | to reach the multiple of four which is the next higher after six
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184 | (eight). If you keep these few rules in mind while working with .bmp
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185 | files it should be easy for you, to master it.
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186 | */
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