通过c++画一个像素点

首先新建一个c++空项目，然后添加tgaimage.h和tgaimage.cpp文件，源代码如下：

tgaimage.h

#ifndef __IMAGE_H__
#define __IMAGE_H__#include <fstream>#pragma pack(push,1)
struct TGA_Header {char idlength;char colormaptype;char datatypecode;short colormaporigin;short colormaplength;char colormapdepth;short x_origin;short y_origin;short width;short height;char  bitsperpixel;char  imagedescriptor;
};
#pragma pack(pop)struct TGAColor {unsigned char bgra[4];unsigned char bytespp;TGAColor() : bgra(), bytespp(1) {for (int i = 0; i < 4; i++) bgra[i] = 0;}TGAColor(unsigned char R, unsigned char G, unsigned char B, unsigned char A = 255) : bgra(), bytespp(4) {bgra[0] = B;bgra[1] = G;bgra[2] = R;bgra[3] = A;}TGAColor(unsigned char v) : bgra(), bytespp(1) {for (int i = 0; i < 4; i++) bgra[i] = 0;bgra[0] = v;}TGAColor(const unsigned char *p, unsigned char bpp) : bgra(), bytespp(bpp) {for (int i = 0; i < (int)bpp; i++) {bgra[i] = p[i];}for (int i = bpp; i < 4; i++) {bgra[i] = 0;}}unsigned char& operator[](const int i) { return bgra[i]; }TGAColor operator *(float intensity) const {TGAColor res = *this;intensity = (intensity > 1.f ? 1.f : (intensity < 0.f ? 0.f : intensity));for (int i = 0; i < 4; i++) res.bgra[i] = bgra[i] * intensity;return res;}
};class TGAImage {
protected:unsigned char* data;int width;int height;int bytespp;bool   load_rle_data(std::ifstream &in);bool unload_rle_data(std::ofstream &out);
public:enum Format {GRAYSCALE = 1, RGB = 3, RGBA = 4};TGAImage();TGAImage(int w, int h, int bpp);TGAImage(const TGAImage &img);bool read_tga_file(const char *filename);bool write_tga_file(const char *filename, bool rle = true);bool flip_horizontally();bool flip_vertically();bool scale(int w, int h);TGAColor get(int x, int y);bool set(int x, int y, TGAColor &c);bool set(int x, int y, const TGAColor &c);~TGAImage();TGAImage & operator =(const TGAImage &img);int get_width();int get_height();int get_bytespp();unsigned char *buffer();void clear();
};#endif //__IMAGE_H__

tgaimage.cpp

#include <iostream>
#include <fstream>
#include <string.h>
#include <time.h>
#include <math.h>
#include "tgaimage.h"TGAImage::TGAImage() : data(NULL), width(0), height(0), bytespp(0) {}TGAImage::TGAImage(int w, int h, int bpp) : data(NULL), width(w), height(h), bytespp(bpp) {unsigned long nbytes = width * height*bytespp;data = new unsigned char[nbytes];memset(data, 0, nbytes);
}TGAImage::TGAImage(const TGAImage &img) : data(NULL), width(img.width), height(img.height), bytespp(img.bytespp) {unsigned long nbytes = width * height*bytespp;data = new unsigned char[nbytes];memcpy(data, img.data, nbytes);
}TGAImage::~TGAImage() {if (data) delete[] data;
}TGAImage & TGAImage::operator =(const TGAImage &img) {if (this != &img) {if (data) delete[] data;width = img.width;height = img.height;bytespp = img.bytespp;unsigned long nbytes = width * height*bytespp;data = new unsigned char[nbytes];memcpy(data, img.data, nbytes);}return *this;
}bool TGAImage::read_tga_file(const char *filename) {if (data) delete[] data;data = NULL;std::ifstream in;in.open(filename, std::ios::binary);if (!in.is_open()) {std::cerr << "can't open file " << filename << "\n";in.close();return false;}TGA_Header header;in.read((char *)&header, sizeof(header));if (!in.good()) {in.close();std::cerr << "an error occured while reading the header\n";return false;}width = header.width;height = header.height;bytespp = header.bitsperpixel >> 3;if (width <= 0 || height <= 0 || (bytespp != GRAYSCALE && bytespp != RGB && bytespp != RGBA)) {in.close();std::cerr << "bad bpp (or width/height) value\n";return false;}unsigned long nbytes = bytespp * width*height;data = new unsigned char[nbytes];if (3 == header.datatypecode || 2 == header.datatypecode) {in.read((char *)data, nbytes);if (!in.good()) {in.close();std::cerr << "an error occured while reading the data\n";return false;}}else if (10 == header.datatypecode || 11 == header.datatypecode) {if (!load_rle_data(in)) {in.close();std::cerr << "an error occured while reading the data\n";return false;}}else {in.close();std::cerr << "unknown file format " << (int)header.datatypecode << "\n";return false;}if (!(header.imagedescriptor & 0x20)) {flip_vertically();}if (header.imagedescriptor & 0x10) {flip_horizontally();}std::cerr << width << "x" << height << "/" << bytespp * 8 << "\n";in.close();return true;
}bool TGAImage::load_rle_data(std::ifstream &in) {unsigned long pixelcount = width * height;unsigned long currentpixel = 0;unsigned long currentbyte = 0;TGAColor colorbuffer;do {unsigned char chunkheader = 0;chunkheader = in.get();if (!in.good()) {std::cerr << "an error occured while reading the data\n";return false;}if (chunkheader < 128) {chunkheader++;for (int i = 0; i < chunkheader; i++) {in.read((char *)colorbuffer.bgra, bytespp);if (!in.good()) {std::cerr << "an error occured while reading the header\n";return false;}for (int t = 0; t < bytespp; t++)data[currentbyte++] = colorbuffer.bgra[t];currentpixel++;if (currentpixel > pixelcount) {std::cerr << "Too many pixels read\n";return false;}}}else {chunkheader -= 127;in.read((char *)colorbuffer.bgra, bytespp);if (!in.good()) {std::cerr << "an error occured while reading the header\n";return false;}for (int i = 0; i < chunkheader; i++) {for (int t = 0; t < bytespp; t++)data[currentbyte++] = colorbuffer.bgra[t];currentpixel++;if (currentpixel > pixelcount) {std::cerr << "Too many pixels read\n";return false;}}}} while (currentpixel < pixelcount);return true;
}bool TGAImage::write_tga_file(const char *filename, bool rle) {unsigned char developer_area_ref[4] = { 0, 0, 0, 0 };unsigned char extension_area_ref[4] = { 0, 0, 0, 0 };unsigned char footer[18] = { 'T','R','U','E','V','I','S','I','O','N','-','X','F','I','L','E','.','\0' };std::ofstream out;out.open(filename, std::ios::binary);if (!out.is_open()) {std::cerr << "can't open file " << filename << "\n";out.close();return false;}TGA_Header header;memset((void *)&header, 0, sizeof(header));header.bitsperpixel = bytespp << 3;header.width = width;header.height = height;header.datatypecode = (bytespp == GRAYSCALE ? (rle ? 11 : 3) : (rle ? 10 : 2));header.imagedescriptor = 0x20; // top-left originout.write((char *)&header, sizeof(header));if (!out.good()) {out.close();std::cerr << "can't dump the tga file\n";return false;}if (!rle) {out.write((char *)data, width*height*bytespp);if (!out.good()) {std::cerr << "can't unload raw data\n";out.close();return false;}}else {if (!unload_rle_data(out)) {out.close();std::cerr << "can't unload rle data\n";return false;}}out.write((char *)developer_area_ref, sizeof(developer_area_ref));if (!out.good()) {std::cerr << "can't dump the tga file\n";out.close();return false;}out.write((char *)extension_area_ref, sizeof(extension_area_ref));if (!out.good()) {std::cerr << "can't dump the tga file\n";out.close();return false;}out.write((char *)footer, sizeof(footer));if (!out.good()) {std::cerr << "can't dump the tga file\n";out.close();return false;}out.close();return true;
}// TODO: it is not necessary to break a raw chunk for two equal pixels (for the matter of the resulting size)
bool TGAImage::unload_rle_data(std::ofstream &out) {const unsigned char max_chunk_length = 128;unsigned long npixels = width * height;unsigned long curpix = 0;while (curpix < npixels) {unsigned long chunkstart = curpix * bytespp;unsigned long curbyte = curpix * bytespp;unsigned char run_length = 1;bool raw = true;while (curpix + run_length < npixels && run_length < max_chunk_length) {bool succ_eq = true;for (int t = 0; succ_eq && t < bytespp; t++) {succ_eq = (data[curbyte + t] == data[curbyte + t + bytespp]);}curbyte += bytespp;if (1 == run_length) {raw = !succ_eq;}if (raw && succ_eq) {run_length--;break;}if (!raw && !succ_eq) {break;}run_length++;}curpix += run_length;out.put(raw ? run_length - 1 : run_length + 127);if (!out.good()) {std::cerr << "can't dump the tga file\n";return false;}out.write((char *)(data + chunkstart), (raw ? run_length * bytespp : bytespp));if (!out.good()) {std::cerr << "can't dump the tga file\n";return false;}}return true;
}TGAColor TGAImage::get(int x, int y) {if (!data || x < 0 || y < 0 || x >= width || y >= height) {return TGAColor();}return TGAColor(data + (x + y * width)*bytespp, bytespp);
}bool TGAImage::set(int x, int y, TGAColor &c) {if (!data || x < 0 || y < 0 || x >= width || y >= height) {return false;}memcpy(data + (x + y * width)*bytespp, c.bgra, bytespp);return true;
}bool TGAImage::set(int x, int y, const TGAColor &c) {if (!data || x < 0 || y < 0 || x >= width || y >= height) {return false;}memcpy(data + (x + y * width)*bytespp, c.bgra, bytespp);return true;
}int TGAImage::get_bytespp() {return bytespp;
}int TGAImage::get_width() {return width;
}int TGAImage::get_height() {return height;
}bool TGAImage::flip_horizontally() {if (!data) return false;int half = width >> 1;for (int i = 0; i < half; i++) {for (int j = 0; j < height; j++) {TGAColor c1 = get(i, j);TGAColor c2 = get(width - 1 - i, j);set(i, j, c2);set(width - 1 - i, j, c1);}}return true;
}bool TGAImage::flip_vertically() {if (!data) return false;unsigned long bytes_per_line = width * bytespp;unsigned char *line = new unsigned char[bytes_per_line];int half = height >> 1;for (int j = 0; j < half; j++) {unsigned long l1 = j * bytes_per_line;unsigned long l2 = (height - 1 - j)*bytes_per_line;memmove((void *)line, (void *)(data + l1), bytes_per_line);memmove((void *)(data + l1), (void *)(data + l2), bytes_per_line);memmove((void *)(data + l2), (void *)line, bytes_per_line);}delete[] line;return true;
}unsigned char *TGAImage::buffer() {return data;
}void TGAImage::clear() {memset((void *)data, 0, width*height*bytespp);
}bool TGAImage::scale(int w, int h) {if (w <= 0 || h <= 0 || !data) return false;unsigned char *tdata = new unsigned char[w*h*bytespp];int nscanline = 0;int oscanline = 0;int erry = 0;unsigned long nlinebytes = w * bytespp;unsigned long olinebytes = width * bytespp;for (int j = 0; j < height; j++) {int errx = width - w;int nx = -bytespp;int ox = -bytespp;for (int i = 0; i < width; i++) {ox += bytespp;errx += w;while (errx >= (int)width) {errx -= width;nx += bytespp;memcpy(tdata + nscanline + nx, data + oscanline + ox, bytespp);}}erry += h;oscanline += olinebytes;while (erry >= (int)height) {if (erry >= (int)height << 1) // it means we jump over a scanlinememcpy(tdata + nscanline + nlinebytes, tdata + nscanline, nlinebytes);erry -= height;nscanline += nlinebytes;}}delete[] data;data = tdata;width = w;height = h;return true;
}

然后添加一个main.cpp文件，代码如下：

#include "tgaimage.h"const TGAColor white = TGAColor(255, 255, 255, 255);
const TGAColor red = TGAColor(255, 0, 0, 255);
int main(int argc, char** argv) {TGAImage image(100, 100, TGAImage::RGB);image.set(52, 41, red);image.flip_vertically(); // i want to have the origin at the left bottom corner of the imageimage.write_tga_file("output.tga"); return 0;
}

可以发现在自己的项目文件夹下生成了一个output.tga文件。

ps或者其他软件打开就可以看见一个像素点了。

参考资料：https://github.com/ssloy/tinyrenderer/wiki/Lesson-0-getting-started

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