asp.net 动态输出透明gif图片
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2024-03-09 11:43:11
查了国内几个中文资料都没解决，最后是在一个英文博客上找到一个可以用的办法。他的解决代码是： 代码 复制代码 代码如下: //存成gif.ashx <%@ webhan...
查了国内几个中文资料都没解决，最后是在一个英文博客上找到一个可以用的办法。
他的解决代码是：
代码
//存成gif.ashx
<%@ webhandler language="c#" class="gif" %>
using system.io;
using system.web;
using system.drawing;
public class gif : ihttphandler {
/// <summary>
/// returns a transparent background gif image from the specified bitmap.
/// </summary>
/// <param name="bitmap">the bitmap to make transparent.</param>
/// <param name="color">the color to make transparent.</param>
/// <returns>new bitmap containing a transparent background gif.</returns>
public bitmap maketransparentgif(bitmap bitmap, color color) {
byte r = color.r;
byte g = color.g;
byte b = color.b;
memorystream fin = new memorystream();
bitmap.save(fin, system.drawing.imaging.imageformat.gif);
memorystream fout = new memorystream((int)fin.length);
int count = 0;
byte[] buf = new byte[256];
byte transparentidx = 0;
fin.seek(0, seekorigin.begin);
//header
count = fin.read(buf, 0, 13);
if ((buf[0] != 71) || (buf[1] != 73) || (buf[2] != 70)) return null; //gif
fout.write(buf, 0, 13);
int i = 0;
if ((buf[10] & 0x80) > 0) {
i = 1 << ((buf[10] & 7) + 1) == 256 ? 256 : 0;
}
for (; i != 0; i--) {
fin.read(buf, 0, 3);
if ((buf[0] == r) && (buf[1] == g) && (buf[2] == b)) {
transparentidx = (byte)(256 - i);
}
fout.write(buf, 0, 3);
}
bool gcepresent = false;
while (true) {
fin.read(buf, 0, 1);
fout.write(buf, 0, 1);
if (buf[0] != 0x21) break;
fin.read(buf, 0, 1);
fout.write(buf, 0, 1);
gcepresent = (buf[0] == 0xf9);
while (true) {
fin.read(buf, 0, 1);
fout.write(buf, 0, 1);
if (buf[0] == 0) break;
count = buf[0];
if (fin.read(buf, 0, count) != count) return null;
if (gcepresent) {
if (count == 4) {
buf[0] |= 0x01;
buf[3] = transparentidx;
}
}
fout.write(buf, 0, count);
}
}
while (count > 0) {
count = fin.read(buf, 0, 1);
fout.write(buf, 0, 1);
}
fin.close();
fout.flush();
return new bitmap(fout);
}
public void processrequest(httpcontext context) {
bitmap transgif = null;
using (bitmap bmp = new bitmap(300, 50)) {
using (graphics g = graphics.fromimage(bmp)) {
g.clear(color.gray);
g.drawstring("transparent gif image",
new font("verdana bold", 14f), brushes.lemonchiffon, 0f, 0f);
bmp.maketransparent(color.gray);
transgif = maketransparentgif(bmp, color.black);
}
}
if (transgif != null) {
context.response.clear();
context.response.contenttype = "image/gif";
transgif.save(context.response.outputstream,
system.drawing.imaging.imageformat.gif);
}
}
public bool isreusable {get {return false;}}
}
测试html文件如下
<!doctype html public "-//w3c//dtd xhtml 1.0 transitional//en" "http://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
</head>
<body style="background:#999">
<img src="gif.ashx" style="position:absolute" />下方的文字
</body>
</html>
他的解决代码是：
代码
复制代码 代码如下:
//存成gif.ashx
<%@ webhandler language="c#" class="gif" %>
using system.io;
using system.web;
using system.drawing;
public class gif : ihttphandler {
/// <summary>
/// returns a transparent background gif image from the specified bitmap.
/// </summary>
/// <param name="bitmap">the bitmap to make transparent.</param>
/// <param name="color">the color to make transparent.</param>
/// <returns>new bitmap containing a transparent background gif.</returns>
public bitmap maketransparentgif(bitmap bitmap, color color) {
byte r = color.r;
byte g = color.g;
byte b = color.b;
memorystream fin = new memorystream();
bitmap.save(fin, system.drawing.imaging.imageformat.gif);
memorystream fout = new memorystream((int)fin.length);
int count = 0;
byte[] buf = new byte[256];
byte transparentidx = 0;
fin.seek(0, seekorigin.begin);
//header
count = fin.read(buf, 0, 13);
if ((buf[0] != 71) || (buf[1] != 73) || (buf[2] != 70)) return null; //gif
fout.write(buf, 0, 13);
int i = 0;
if ((buf[10] & 0x80) > 0) {
i = 1 << ((buf[10] & 7) + 1) == 256 ? 256 : 0;
}
for (; i != 0; i--) {
fin.read(buf, 0, 3);
if ((buf[0] == r) && (buf[1] == g) && (buf[2] == b)) {
transparentidx = (byte)(256 - i);
}
fout.write(buf, 0, 3);
}
bool gcepresent = false;
while (true) {
fin.read(buf, 0, 1);
fout.write(buf, 0, 1);
if (buf[0] != 0x21) break;
fin.read(buf, 0, 1);
fout.write(buf, 0, 1);
gcepresent = (buf[0] == 0xf9);
while (true) {
fin.read(buf, 0, 1);
fout.write(buf, 0, 1);
if (buf[0] == 0) break;
count = buf[0];
if (fin.read(buf, 0, count) != count) return null;
if (gcepresent) {
if (count == 4) {
buf[0] |= 0x01;
buf[3] = transparentidx;
}
}
fout.write(buf, 0, count);
}
}
while (count > 0) {
count = fin.read(buf, 0, 1);
fout.write(buf, 0, 1);
}
fin.close();
fout.flush();
return new bitmap(fout);
}
public void processrequest(httpcontext context) {
bitmap transgif = null;
using (bitmap bmp = new bitmap(300, 50)) {
using (graphics g = graphics.fromimage(bmp)) {
g.clear(color.gray);
g.drawstring("transparent gif image",
new font("verdana bold", 14f), brushes.lemonchiffon, 0f, 0f);
bmp.maketransparent(color.gray);
transgif = maketransparentgif(bmp, color.black);
}
}
if (transgif != null) {
context.response.clear();
context.response.contenttype = "image/gif";
transgif.save(context.response.outputstream,
system.drawing.imaging.imageformat.gif);
}
}
public bool isreusable {get {return false;}}
}
测试html文件如下
复制代码 代码如下:
<!doctype html public "-//w3c//dtd xhtml 1.0 transitional//en" "http://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
</head>
<body style="background:#999">
<img src="gif.ashx" style="position:absolute" />下方的文字
</body>
</html>
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