C++ Builder / TCanvas > 円をセクターに分割して、グラデーションを塗る実装

動作環境

C++ Builder XE4

• 円を描く
• 20個のsectorsに分割する
• RGB値のBを変化させながらsectorを塗る

Unit1.cpp

//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
}
//---------------------------------------------------------------------------

void __fastcall TForm1::drawRadialLine(double angle_deg)
{
    TRect R = Image1->ClientRect;

    double radius = (R.right - R.left) / 2;
    int center_x = (R.left + R.right) / 2;
    int center_y = (R.top + R.bottom) / 2;

    Image1->Canvas->MoveTo(center_x, center_y);

    int to_x = radius * Cos(angle_deg * M_PI / 180.0);
    int to_y = radius * Sin(angle_deg * M_PI / 180.0);
    to_x += center_x;
    to_y += center_y;
    Image1->Canvas->LineTo(to_x, to_y);
}

void __fastcall TForm1::fillSector(double angle_deg, double width_deg)
{
    TRect R = Image1->ClientRect;
    double radius = (R.right - R.left) / 2;

    radius = 0.7 * radius; // to get inside the sector (0.7: arbitrary)
    double wrk_ang = angle_deg + width_deg / 2.0; // to get inside the sector

    int center_x = (R.left + R.right) / 2;
    int center_y = (R.top + R.bottom) / 2;

    int pt_x = radius * Cos(wrk_ang * M_PI / 180.0);
    int pt_y = radius * Sin(wrk_ang * M_PI / 180.0);
    pt_x += center_x;
    pt_y += center_y;

    Image1->Canvas->Brush->Color = RGB(0, 0, 255 * angle_deg / 360.0);
    Image1->Canvas->FloodFill(pt_x, pt_y, clBlack, fsBorder);

    // String msg = IntToStr(pt_x) + L"-" + IntToStr(pt_y) + L": " + FloatToStr(angle_deg);
    // OutputDebugString(msg.c_str());
}

void __fastcall TForm1::drawOnImage(void)
{
    // 1. draw circle
    TRect R = Image1->ClientRect;
    //                      X1,     Y1     X2       Y2
    Image1->Canvas->Ellipse(R.left, R.top, R.right, R.bottom);

    // 2. draw line in radial direction
    static const int kNumAngles = 20;

    for(int idx=0; idx < kNumAngles; idx++) {
        double ang_deg = (360.0 / (double)kNumAngles) * idx;
        drawRadialLine(ang_deg);
    }

    // 3.. fill the sectors
    for(int idx=0; idx < kNumAngles; idx++) {
        double ang_deg = (360.0 / (double)kNumAngles) * idx;
        fillSector(ang_deg, /* width_deg=*/(360.0 / kNumAngles));
    }
}

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    drawOnImage();
}
//---------------------------------------------------------------------------