C#+OpenGL+FreeType显示3D文字(3) - 用PointSprite绘制文字

[b]C#+OpenGL+FreeType显示3D文字(3) - 用PointSprite绘制文字 [/b]

上一篇实现了把文字绘制到OpenGL窗口，但实质上只是把含有文字的贴图贴到矩形模型上。本篇我们介绍用PointSprite绘制文字，这可以只用1个点绘制文字，并确保文字始终面相窗口。用PointSprite绘制的文字，其大小范围有限，本篇提供的Demo中，Max Row Width最大只有256。现在能够绘制少量的文字，为其指定的位置的过程与为一个点指定位置的过程是相同的，所以此方式的应用范围还是比较广的。

基本流程

与前文相同的是仍然用GLSL+VBO+贴图来绘制。PointSprite只是Enable了一些OpenGL开关，然后把贴图贴到一个Point图元上。

/// <summary>
/// 为指定的字符串生成贴图。
/// </summary>
/// <param name="fontResource"></param>
/// <param name="content"></param>
/// <param name="fontSize"></param>
/// <param name="maxRowWidth"></param>
/// <returns></returns>
public static System.Drawing.Bitmap GenerateBitmapForString(this FontResource fontResource,
string content, int fontSize, int maxRowWidth)
{
// step 1: get totalLength
int totalLength = 0;
{
int glyphsLength = 0;
for (int i = 0; i < content.Length; i++)
{
char c = content[i];
CharacterInfo cInfo;
if (fontResource.CharInfoDict.TryGetValue(c, out cInfo))
{
int glyphWidth = cInfo.width;
glyphsLength += glyphWidth;
}
//else
//{ throw new Exception(string.Format("Not support for display the char [{0}]", c)); }
}

//glyphsLength = (glyphsLength * this.fontSize / FontResource.Instance.FontHeight);
int interval = fontResource.FontHeight / 10; if (interval < 1) { interval = 1; }
totalLength = glyphsLength + interval * (content.Length - 1);
}

// step 2: setup contentBitmap
System.Drawing.Bitmap contentBitmap = null;
{
int interval = fontResource.FontHeight / 10; if (interval < 1) { interval = 1; }
//int totalLength = glyphsLength + interval * (content.Length - 1);
int currentTextureWidth = 0;
int currentWidthPos = 0;
int currentHeightPos = 0;
if (totalLength * fontSize > maxRowWidth * fontResource.FontHeight)// 超过1行能显示的内容
{
currentTextureWidth = maxRowWidth * fontResource.FontHeight / fontSize;

int lineCount = (totalLength - 1) / currentTextureWidth + 1;
// 确保整篇文字的高度在贴图中间。
currentHeightPos = (currentTextureWidth - fontResource.FontHeight * lineCount) / 2;
//- FontResource.Instance.FontHeight / 2;
}
else//只在一行内即可显示所有字符
{
if (totalLength >= fontResource.FontHeight)
{
currentTextureWidth = totalLength;

// 确保整篇文字的高度在贴图中间。
currentHeightPos = (currentTextureWidth - fontResource.FontHeight) / 2;
//- FontResource.Instance.FontHeight / 2;
}
else
{
currentTextureWidth = fontResource.FontHeight;

currentWidthPos = (currentTextureWidth - totalLength) / 2;
//glyphsLength = fontResource.FontHeight;
}
}

//this.textureWidth = textureWidth * this.fontSize / FontResource.Instance.FontHeight;
//currentWidthPosition = currentWidthPosition * this.fontSize / FontResource.Instance.FontHeight;
//currentHeightPosition = currentHeightPosition * this.fontSize / FontResource.Instance.FontHeight;

contentBitmap = new Bitmap(currentTextureWidth, currentTextureWidth);
Graphics gContentBitmap = Graphics.FromImage(contentBitmap);
Bitmap bigBitmap = fontResource.FontBitmap;
for (int i = 0; i < content.Length; i++)
{
char c = content[i];
CharacterInfo cInfo;
if (fontResource.CharInfoDict.TryGetValue(c, out cInfo))
{
if (currentWidthPos + cInfo.width > contentBitmap.Width)
{
currentWidthPos = 0;
currentHeightPos += fontResource.FontHeight;
}

gContentBitmap.DrawImage(bigBitmap,
new Rectangle(currentWidthPos, currentHeightPos, cInfo.width, fontResource.FontHeight),
new Rectangle(cInfo.xoffset, cInfo.yoffset, cInfo.width, fontResource.FontHeight),
GraphicsUnit.Pixel);

currentWidthPos += cInfo.width + interval;
}
}
gContentBitmap.Dispose();
//contentBitmap.Save("PointSpriteStringElement-contentBitmap.png");
System.Drawing.Bitmap bmp = null;
if (totalLength * fontSize > maxRowWidth * fontResource.FontHeight)// 超过1行能显示的内容
{
bmp = (System.Drawing.Bitmap)contentBitmap.GetThumbnailImage(
maxRowWidth, maxRowWidth, null, IntPtr.Zero);
}
else//只在一行内即可显示所有字符
{
if (totalLength >= fontResource.FontHeight)
{
bmp = (System.Drawing.Bitmap)contentBitmap.GetThumbnailImage(
totalLength * fontSize / fontResource.FontHeight,
totalLength * fontSize / fontResource.FontHeight,
null, IntPtr.Zero);

}
else
{
bmp = (System.Drawing.Bitmap)contentBitmap.GetThumbnailImage(
fontSize, fontSize, null, IntPtr.Zero);
}
}
contentBitmap.Dispose();
contentBitmap = bmp;
//contentBitmap.Save("PointSpriteStringElement-contentBitmap-scaled.png");
}

return contentBitmap;

}

计算字符串贴图

缺陷

用PointSprite绘制的文字，其大小范围有限，本篇提供的Demo中，Max Row Width最大只有256。

总结

现在能够绘制少量的文字，为其指定的位置的过程与为一个点指定位置的过程是相同的，所以此方式的应用范围还是比较广的。

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