C++ Graphics Programming Algorithm Analysis

C Graphics programming algorithms include: Bresenham straight line algorithm: draw straight lines efficiently. Circular scanning algorithm: fill any shape contour. Scan fill algorithm: Efficiently fill the area between contours.

C Graphics Programming Algorithm Exquisite Analysis

Introduction

Graphics programming algorithm in Indispensable in modern software development, they allow us to create interactive and visually pleasing applications. C is a popular language for graphics programming, and this article will delve into some useful algorithms.

Bresenham Straight Line Algorithm

Bresenham Straight Line Algorithm is used to draw straight lines in the fastest way. It uses integer arithmetic, making the drawing process efficient and accurate.

void drawLine(int x1, int y1, int x2, int y2) {
  int dx = x2 - x1;
  int dy = y2 - y1;
  int d = 2 * dy - dx;
  int y = y1;
  for (int x = x1; x <= x2; x++) {
    plot(x, y);
    if (d < 0) {
      d += 2 * dy;
    } else {
      d += 2 * (dy - dx);
      y++;
    }
  }
}

Circular scanning algorithm

The circular scanning algorithm is used to fill the outline of any shape. It works by moving a scanline along the shape boundary and filling the area beneath it.

void fill(int x1, int y1, int x2, int y2, int color) {
  for (int y = y1; y <= y2; y++) {
    int x_min = INT_MAX, x_max = INT_MIN;
    for (int x = x1; x <= x2; x++) {
      if (isInsideBoundary(x, y)) {
        x_min = min(x_min, x);
        x_max = max(x_max, x);
      }
    }
    for (int x = x_min; x <= x_max; x++) {
      plot(x, y, color);
    }
  }
}

Scan-to-fill algorithm

The scan-to-fill algorithm is an efficient filling algorithm that works by scanning the vertical sides of an outline and filling the area between them.

void scanFill(int x1, int y1, int x2, int y2, int color) {
  int edgeTable[MAX_SIZE][2];  // 存储轮廓边
  int edgeCount = 0;

  // 构建边表
  for (int x = x1; x <= x2; x++) {
    int y_min = INT_MAX, y_max = INT_MIN;
    for (int y = y1; y <= y2; y++) {
      if (isInsideBoundary(x, y)) {
        y_min = min(y_min, y);
        y_max = max(y_max, y);
      }
    }
    if (y_min != INT_MAX) {
      edgeTable[edgeCount][0] = x;
      edgeTable[edgeCount][1] = y_min;
      edgeCount++;
      edgeTable[edgeCount][0] = x;
      edgeTable[edgeCount][1] = y_max;
      edgeCount++;
    }
  }

  // 扫描填充
  for (int j = 0; j < edgeCount; j += 2) {
    for (int x = edgeTable[j][0]; x <= edgeTable[j + 1][0]; x++) {
      plot(x, edgeTable[j][1], color);
      plot(x, edgeTable[j + 1][1], color);
    }
  }
}

Practical case

The following is a C code example containing the above algorithm, showing how to draw a straight line and fill a rectangular area with the scan and fill algorithm:

#include <iostream>
#include <cmath>

using namespace std;

void plot(int x, int y, int color = 0xFFFFFFFF) {
  // 绘制像素的代码
}

int main() {
  // 绘制一条线
  drawLine(0, 0, 500, 500);

  // 填充矩形
  fill(100, 100, 400, 400, 0xFF0000);

  return 0;
}

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