Overview

The CDC (Device Context) class in MFC provides comprehensive functionality for text rendering operations. As a wrapper around Windows GDI functions, CDC handles everything from text positioning to font management.

Core Text Rendering Functions

DrawText

The DrawText method formats and draws text within a specified bounding rectangle. It supports various alignment options and automatic text wrapping.

int DrawText(
    LPCTSTR textBuffer,    // pointer to text content
    int characterCount,    // number of characters to render
    LPRECT boundingBox,    // pointer to RECT structure
    UINT formattingFlags   // layout and display options
);

Formatting Flags

Alignment options control how text positions within the rectangle:

• DT_CENTER: Horizontal centering
• DT_LEFT: Left alignment
• DT_RIGHT: Right alignment
• DT_VCENTER: Vertical centering
• DT_TOP: Top alignment
• DT_BOTTOM: Bottom alignment

Line breaking behavior options:

• DT_SINGLELINE: Forces single-line rendering, truncating overflow
• DT_WORDBREAK: Breaks lines at word boundaries
• DT_WORDELLIPSIS: Truncates with ellipsis at the last complete word
• DT_PATH_ELLIPSIS: Adds elipsis in the middle of path strings

Special rendering modes:

• DT_CALCRECT: Calculates rectangle dimensions without drawing
• DT_EXPANDTABS: Converts tab characters to spaces
• DT_NOPREFIX: Disables mnemonic character processing
• DT_END_ELLIPSIS: Places ellipsis at the text end

Combine multiple flags using the bitwise OR operator. For instance, DT_CENTER | DT_VCENTER centers text both horizontally and vertically.

TextOut

The TextOut method renders a single line of text starting at a specified coordinate:

BOOL TextOut(
    int startX,           // horizontal starting position
    int startY,           // vertical starting position
    LPCTSTR textContent,  // pointer to null-terminated string
    int charCount         // character count (usually -1 for auto-detect)
);

The character count parameter can typical be omitted when working with null-terminated strings.

Text Styling Functions

SetTextColor

Sets the foreground color for subsequant text operations:

COLORREF SetTextColor(
    COLORREF newColor   // RGB color value
);

SetBkColor

Defines the background color behind rendered text:

COLORREF SetBkColor(
    COLORREF backgroundColor   // RGB color value
);

GetTextMetrics

Retrieves detailed information about the currently selected font, including character dimensions and baseline data:

BOOL GetTextMetrics(
    LPTEXTMETRIC fontMetrics   // pointer to TEXTMETRIC structure
);

This function proves essential when calculating precise text positioning or spacing requirements.

Implementation Workflow

Standard practice involves configuring text attributes before rendering:

CDC* deviceContext = GetDC();
deviceContext->SetTextColor(RGB(255, 0, 0));
deviceContext->SetBkColor(RGB(255, 255, 255));
deviceContext->TextOut(10, 20, _T("Sample Text"), -1);

TEXTMETRIC tm;
deviceContext->GetTextMetrics(&tm);
// Use tm values for subsequent positioning

ReleaseDC(deviceContext);

When modifying device context resources, always restore original settings after completing text operations to prevent resource leaks and unexpected visual behavior in other application areas.

Character Encoding Notes

MFC provides both ANSI and Unicode variants of text functions. DrawTextA handles ANSI strings while DrawTextW manages Unicode strings. Most modern projects use Unicode by default, and the framework automatically selects the appropriate version based on project configuration settings.