glActiveTexture 默认行为与预期不符
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【中文标题】glActiveTexture 默认行为与预期不符【英文标题】：glActiveTexture default behavior not as anticipated 【发布时间】：2018-03-28 19:21:04 【问题描述】：我想澄清一下默认的 OpenGL 行为。据我了解，默认的活动纹理单元为 0 (GL_TEXTURE0)，除非通过 glActiveTexture 明确更改，否则将保持不变。
我之所以这么问，是因为我遇到了无法解释且有问题的行为。在加载并将纹理绑定到GL_TEXTURE_2D（假设GL_TEXTURE0 处于活动状态）后，我无法显示它，直到我将活动纹理设置为GL_TEXTURE1。甚至在加载后第一次绑定之前显式调用glActiveTexture(GL_TEXTUREX)，然后在我在绘图期间使用它时重复此调用也无济于事。仅当我在绑定和分配给着色器之前调用 glActiveTexture(GL_TEXTURE1) 时才会显示纹理。
当我尝试使用更多纹理时重复此过程，我必须根据我加载和第一次绑定纹理的顺序显式设置每个 glActiveTexture(GL_TEXTURE...)，然后再绑定它们并将它们分配给着色器。即使我没有使用我加载的第一个纹理进行绘制，我仍然必须调用glActiveTexture(GL_TEXTURE2)...而不是GL_TEXTURE1，或者更好的是GL_TEXTURE0，因为我什至还没有调用glActiveTexture(...)观点。我认为后者是根据 GL 规范应该发生的。
https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glActiveTexture.xhtml
这是司机主义吗？
戴尔 Precision M6800、nV K2200M、GL 4.1 和 3.3。
更新：孤立的例子。
#include <Windows.h>
#include <gl\GL.h>
#include "glext.h"
#include "wglext.h"
#include <vector>
#include <memory>
#include <atlimage.h>
namespace
class GLFunc
public:
GLFunc()
glCreateProgram = (PFNGLCREATEPROGRAMPROC)wglGetProcAddress("glCreateProgram");
glCreateShader = (PFNGLCREATESHADERPROC)wglGetProcAddress("glCreateShader");
glShaderSource = (PFNGLSHADERSOURCEPROC)wglGetProcAddress("glShaderSource");
glCompileShader = (PFNGLCOMPILESHADERPROC)wglGetProcAddress("glCompileShader");
glAttachShader = (PFNGLATTACHSHADERPROC)wglGetProcAddress("glAttachShader");
glDetachShader = (PFNGLDETACHSHADERPROC)wglGetProcAddress("glDetachShader");
glLinkProgram = (PFNGLLINKPROGRAMPROC)wglGetProcAddress("glLinkProgram");
glUseProgram = (PFNGLUSEPROGRAMPROC)wglGetProcAddress("glUseProgram");
glGenFramebuffers = (PFNGLGENFRAMEBUFFERSPROC)wglGetProcAddress("glGenFramebuffers");
glBindFramebuffer = (PFNGLBINDFRAMEBUFFERPROC)wglGetProcAddress("glBindFramebuffer");
glGenRenderbuffers = (PFNGLGENRENDERBUFFERSPROC)wglGetProcAddress("glGenRenderbuffers");
glBindRenderbuffer = (PFNGLBINDRENDERBUFFERPROC)wglGetProcAddress("glBindRenderbuffer");
glRenderbufferStorage = (PFNGLRENDERBUFFERSTORAGEPROC)wglGetProcAddress("glRenderbufferStorage");
glFramebufferRenderbuffer = (PFNGLFRAMEBUFFERRENDERBUFFERPROC)wglGetProcAddress("glFramebufferRenderbuffer");
glFramebufferTexture = (PFNGLFRAMEBUFFERTEXTUREPROC)wglGetProcAddress("glFramebufferTexture");
glDrawBuffers = (PFNGLDRAWBUFFERSPROC)wglGetProcAddress("glDrawBuffers");
glCheckFramebufferStatus = (PFNGLCHECKFRAMEBUFFERSTATUSPROC)wglGetProcAddress("glCheckFramebufferStatus");
glGenVertexArrays = (PFNGLGENVERTEXARRAYSPROC)wglGetProcAddress("glGenVertexArrays");
glBindBuffer = (PFNGLBINDBUFFERPROC)wglGetProcAddress("glBindBuffer");
glBufferData = (PFNGLBUFFERDATAPROC)wglGetProcAddress("glBufferData");
glDeleteFramebuffers = (PFNGLDELETEFRAMEBUFFERSPROC)wglGetProcAddress("glDeleteFramebuffers");
glDeleteRenderbuffers = (PFNGLDELETERENDERBUFFERSPROC)wglGetProcAddress("glDeleteRenderbuffers");
glDeleteVertexArrays = (PFNGLDELETEVERTEXARRAYSPROC)wglGetProcAddress("glDeleteVertexArrays");
glGetShaderiv = (PFNGLGETSHADERIVPROC)wglGetProcAddress("glGetShaderiv");
glGetShaderInfoLog = (PFNGLGETSHADERINFOLOGPROC)wglGetProcAddress("glGetShaderInfoLog");
glGetProgramiv = (PFNGLGETPROGRAMIVPROC)wglGetProcAddress("glGetProgramiv");
glGetProgramInfoLog = (PFNGLGETPROGRAMINFOLOGPROC)wglGetProcAddress("glGetProgramInfoLog");
glGenBuffers = (PFNGLGENBUFFERSPROC)wglGetProcAddress("glGenBuffers");
glEnableVertexAttribArray = (PFNGLENABLEVERTEXATTRIBARRAYPROC)wglGetProcAddress("glEnableVertexAttribArray");
glVertexAttribPointer = (PFNGLVERTEXATTRIBPOINTERPROC)wglGetProcAddress("glVertexAttribPointer");
glBindVertexArray = (PFNGLBINDVERTEXARRAYPROC)wglGetProcAddress("glBindVertexArray");
glGetUniformLocation = (PFNGLGETUNIFORMLOCATIONPROC)wglGetProcAddress("glGetUniformLocation");
glUniformMatrix2fv = (PFNGLUNIFORMMATRIX2FVPROC)wglGetProcAddress("glUniformMatrix2fv");
glUniformMatrix3fv = (PFNGLUNIFORMMATRIX3FVPROC)wglGetProcAddress("glUniformMatrix3fv");
glUniformMatrix4fv = (PFNGLUNIFORMMATRIX4FVPROC)wglGetProcAddress("glUniformMatrix4fv");
glUniform1f = (PFNGLUNIFORM1FPROC)wglGetProcAddress("glUniform1f");
glUniform2f = (PFNGLUNIFORM2FPROC)wglGetProcAddress("glUniform2f");
glUniform3f = (PFNGLUNIFORM3FPROC)wglGetProcAddress("glUniform3f");
glUniform4f = (PFNGLUNIFORM4FPROC)wglGetProcAddress("glUniform4f");
glUniform1i = (PFNGLUNIFORM1IPROC)wglGetProcAddress("glUniform1i");
glUniform2i = (PFNGLUNIFORM2IPROC)wglGetProcAddress("glUniform2i");
glUniform3i = (PFNGLUNIFORM3IPROC)wglGetProcAddress("glUniform3i");
glUniform4i = (PFNGLUNIFORM4IPROC)wglGetProcAddress("glUniform4i");
glActiveTexture = (PFNGLACTIVETEXTUREPROC)wglGetProcAddress("glActiveTexture");
glDeleteShader = (PFNGLDELETESHADERPROC)wglGetProcAddress("glDeleteShader");
PFNGLCREATEPROGRAMPROC glCreateProgram;
PFNGLCREATESHADERPROC glCreateShader;
PFNGLSHADERSOURCEPROC glShaderSource;
PFNGLCOMPILESHADERPROC glCompileShader;
PFNGLATTACHSHADERPROC glAttachShader;
PFNGLDETACHSHADERPROC glDetachShader;
PFNGLLINKPROGRAMPROC glLinkProgram;
PFNGLUSEPROGRAMPROC glUseProgram;
PFNGLGENFRAMEBUFFERSPROC glGenFramebuffers;
PFNGLBINDFRAMEBUFFERPROC glBindFramebuffer;
PFNGLGENRENDERBUFFERSPROC glGenRenderbuffers;
PFNGLBINDRENDERBUFFERPROC glBindRenderbuffer;
PFNGLRENDERBUFFERSTORAGEPROC glRenderbufferStorage;
PFNGLFRAMEBUFFERRENDERBUFFERPROC glFramebufferRenderbuffer;
PFNGLFRAMEBUFFERTEXTUREPROC glFramebufferTexture;
PFNGLDRAWBUFFERSPROC glDrawBuffers;
PFNGLCHECKFRAMEBUFFERSTATUSPROC glCheckFramebufferStatus;
PFNGLGENVERTEXARRAYSPROC glGenVertexArrays;
PFNGLBINDBUFFERPROC glBindBuffer;
PFNGLBUFFERDATAPROC glBufferData;
PFNGLDELETEFRAMEBUFFERSPROC glDeleteFramebuffers;
PFNGLDELETERENDERBUFFERSPROC glDeleteRenderbuffers;
PFNGLDELETEVERTEXARRAYSPROC glDeleteVertexArrays;
PFNGLGETSHADERIVPROC glGetShaderiv;
PFNGLGETSHADERINFOLOGPROC glGetShaderInfoLog;
PFNGLGETPROGRAMIVPROC glGetProgramiv;
PFNGLGETPROGRAMINFOLOGPROC glGetProgramInfoLog;
PFNGLGENBUFFERSPROC glGenBuffers;
PFNGLENABLEVERTEXATTRIBARRAYPROC glEnableVertexAttribArray;
PFNGLVERTEXATTRIBPOINTERPROC glVertexAttribPointer;
PFNGLBINDVERTEXARRAYPROC glBindVertexArray;
PFNGLGETUNIFORMLOCATIONPROC glGetUniformLocation;
PFNGLUNIFORMMATRIX2FVPROC glUniformMatrix2fv;
PFNGLUNIFORMMATRIX3FVPROC glUniformMatrix3fv;
PFNGLUNIFORMMATRIX4FVPROC glUniformMatrix4fv;
PFNGLUNIFORM1FPROC glUniform1f;
PFNGLUNIFORM2FPROC glUniform2f;
PFNGLUNIFORM3FPROC glUniform3f;
PFNGLUNIFORM4FPROC glUniform4f;
PFNGLUNIFORM1IPROC glUniform1i;
PFNGLUNIFORM2IPROC glUniform2i;
PFNGLUNIFORM3IPROC glUniform3i;
PFNGLUNIFORM4IPROC glUniform4i;
PFNGLACTIVETEXTUREPROC glActiveTexture;
PFNGLDELETESHADERPROC glDeleteShader;
;
static HGLRC hglrc_;
static GLFunc* gl_;
unsigned int points_;
unsigned int uvs_;
unsigned int indexes_;
unsigned int vao_;
unsigned int calibrationTexture_;
unsigned int vertexShader_;
unsigned int fragmentShader_;
unsigned int programID_;
struct Vector3
Vector3(float x, float y, float z)
: x_(x), y_(y), z_(z)
float x_;
float y_;
float z_;
;
struct Vector2
Vector2(float x, float y)
: x_(x), y_(y)
float x_;
float y_;
;
struct Texture
Texture(unsigned int width, unsigned int height)
: width_(width), height_(height)
bits_.insert(bits_.end(), width*height * 3, 0);
unsigned char* GetTexel(unsigned int x, unsigned int y)
return &bits_[((x * height_) + y)*3];
unsigned int width_;
unsigned int height_;
std::vector<unsigned char> bits_;
;
unsigned int CompileVertexShader(const std::string& sourceCode)
GLint result = GL_FALSE;
GLuint vertexShaderID = gl_->glCreateShader(GL_VERTEX_SHADER);
const char* src = sourceCode.c_str();
gl_->glShaderSource(vertexShaderID, 1, &src, NULL);
gl_->glCompileShader(vertexShaderID);
gl_->glGetShaderiv(vertexShaderID, GL_COMPILE_STATUS, &result);
if (result == GL_FALSE)
int infoLogLength;
gl_->glGetShaderiv(vertexShaderID, GL_INFO_LOG_LENGTH, &infoLogLength);
std::vector<GLchar> error(infoLogLength);
gl_->glGetShaderInfoLog(vertexShaderID, infoLogLength, &infoLogLength, &error[0]);
std::string errStr(&error[0], error.size());
OutputDebugString(errStr.c_str());
return 0;
return vertexShaderID;
unsigned int CompileFragmentShader(const std::string& sourceCode)
GLint result = GL_FALSE;
GLuint fragmentShaderID = gl_->glCreateShader(GL_FRAGMENT_SHADER);
const char* src = sourceCode.c_str();
gl_->glShaderSource(fragmentShaderID, 1, &src, NULL);
gl_->glCompileShader(fragmentShaderID);
gl_->glGetShaderiv(fragmentShaderID, GL_COMPILE_STATUS, &result);
if (result == GL_FALSE)
int infoLogLength;
gl_->glGetShaderiv(fragmentShaderID, GL_INFO_LOG_LENGTH, &infoLogLength);
std::vector<GLchar> error(infoLogLength);
gl_->glGetShaderInfoLog(fragmentShaderID, infoLogLength, &infoLogLength, &error[0]);
std::string errStr(&error[0], error.size());
OutputDebugString(errStr.c_str());
return 0;
return fragmentShaderID;
unsigned int LinkShaderProgram(unsigned int vertexShader, unsigned int fragmentShader)
// attempt to link the program...
GLint result = GL_FALSE;
unsigned int programID = gl_->glCreateProgram();
gl_->glAttachShader(programID, vertexShader);
gl_->glAttachShader(programID, fragmentShader);
gl_->glLinkProgram(programID);
gl_->glGetProgramiv(programID, GL_LINK_STATUS, &result);
if (result == GL_FALSE)
int InfoLogLength;
gl_->glGetProgramiv(programID, GL_INFO_LOG_LENGTH, &InfoLogLength);
std::vector<GLchar> error(InfoLogLength);
gl_->glGetProgramInfoLog(programID, InfoLogLength, &InfoLogLength, &error[0]);
std::string errStr(&error[0], error.size());
OutputDebugString(errStr.c_str());
return 0;
gl_->glDetachShader(programID, vertexShader);
gl_->glDetachShader(programID, fragmentShader);
return programID;
void SetUniform(const std::string& name, unsigned int ID)
int location = gl_->glGetUniformLocation(programID_, name.c_str());
if (location < 0)
OutputDebugString("Unable to find uniform location :(");
else
gl_->glUniform1i(location, ID);
std::shared_ptr<Texture> LoadTexture(const std::string& filename)
CImage image;
image.Load(filename.c_str());
std::shared_ptr<Texture> texture(new Texture(image.GetWidth(), image.GetHeight()));
for (int y = image.GetHeight() - 1; y >= 0; --y)
for (int x = 0; x < image.GetWidth(); ++x)
unsigned char* target = texture->GetTexel(x, y);
unsigned char* source = reinterpret_cast<unsigned char*>(image.GetPixelAddress(x, y));
for ( unsigned int c = 0; c < 3; ++c )
*(target+c) = *(source+c);
return texture;
extern "C" __declspec(dllexport) int OpenGLInit(void* hdc)
// We need to create a context or get an existing one that fits the supplied context.
// first check we have a valid device context
if (!hdc)
return 1;
HDC hDC = static_cast<HDC>(hdc);
if (!hDC)
return 2;
// we then need to get a valid DC...
PIXELFORMATDESCRIPTOR pfd;
memset(&pfd, 0, sizeof(PIXELFORMATDESCRIPTOR));
pfd.nSize = sizeof(PIXELFORMATDESCRIPTOR);
pfd.nVersion = 1;
pfd.dwFlags = PFD_DOUBLEBUFFER | PFD_SUPPORT_OPENGL | PFD_DRAW_TO_WINDOW;
pfd.iPixelType = PFD_TYPE_RGBA;
pfd.cColorBits = 32;
pfd.cDepthBits = 32;
pfd.cStencilBits = 8;
pfd.iLayerType = PFD_MAIN_PLANE;
int nPixelFormat = ChoosePixelFormat(hDC, &pfd);
if (nPixelFormat == 0)
return 3;
if (!SetPixelFormat(hDC, nPixelFormat, &pfd))
return 4;
HGLRC tempContext = wglCreateContext(hDC);
wglMakeCurrent(hDC, tempContext);
int attribs[] =
WGL_CONTEXT_MAJOR_VERSION_ARB, 4,
WGL_CONTEXT_MINOR_VERSION_ARB, 1,
WGL_CONTEXT_FLAGS_ARB, 0,
0
;
PFNWGLCREATECONTEXTATTRIBSARBPROC wglCreateContextAttribsARB = (PFNWGLCREATECONTEXTATTRIBSARBPROC)wglGetProcAddress("wglCreateContextAttribsARB");
if (wglCreateContextAttribsARB)
hglrc_ = wglCreateContextAttribsARB(hDC, 0, attribs);
wglMakeCurrent(NULL, NULL);
wglDeleteContext(tempContext);
if (!wglMakeCurrent(hDC, hglrc_))
return 5;
// Initialise the functions..
gl_ = new GLFunc();
// Cache the geometry for a quad
float v = 1.0f;
std::vector<Vector3> quadPoints = std::initializer_list<Vector3>(
Vector3(-v, -v, 0),
Vector3(v, -v, 0),
Vector3(v, v, 0),
Vector3(-v, v, 0)
);
std::vector<Vector2> quadUVs = std::initializer_list<Vector2>(
Vector2(0, 0),
Vector2(1.0f, 0),
Vector2(1.0f, 1.0f),
Vector2(0, 1.0f)
);
std::vector<unsigned int> quadIndexes = std::initializer_list<unsigned int>(
0, 1, 2, 2, 3, 0
);
gl_->glGenVertexArrays(1, &vao_);
gl_->glBindVertexArray(vao_);
// Cache the points...
gl_->glGenBuffers(1, &points_);
gl_->glBindBuffer(GL_ARRAY_BUFFER, points_);
gl_->glBufferData(GL_ARRAY_BUFFER, sizeof(float) * 3 * quadPoints.size(), &quadPoints[0].x_, GL_STATIC_DRAW);
gl_->glEnableVertexAttribArray(0);
gl_->glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
// Cache the UVs...
gl_->glGenBuffers(1, &uvs_);
gl_->glBindBuffer(GL_ARRAY_BUFFER, uvs_);
gl_->glBufferData(GL_ARRAY_BUFFER, sizeof(float) * quadUVs.size() * 2, &quadUVs[0].x_, GL_STATIC_DRAW);
gl_->glEnableVertexAttribArray(1);
gl_->glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, 0);
// Cache the indexes...
gl_->glGenBuffers(1, &indexes_);
gl_->glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexes_);
gl_->glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(unsigned int) * quadIndexes.size(), &quadIndexes[0], GL_STATIC_DRAW);
gl_->glBindBuffer(GL_ARRAY_BUFFER, NULL);
gl_->glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, NULL);
gl_->glBindVertexArray(NULL);
// Load the texture...
std::shared_ptr<Texture> calibrationImage = LoadTexture("uvgrid.jpg");
glGenTextures(1, &calibrationTexture_);
glBindTexture(GL_TEXTURE_2D, calibrationTexture_);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, calibrationImage->width_, calibrationImage->height_, 0, GL_RGB, GL_UNSIGNED_BYTE, &calibrationImage->bits_[0]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glBindTexture(GL_TEXTURE_2D, NULL);
// Compile the shaders
const char* fragmentSource = R"(
#version 410 core
uniform sampler2D quadTexture;
in vec2 UV;
out vec3 COLOUR;
void main()
//COLOUR = vec3(UV.st, 0);
COLOUR = texture(quadTexture, UV).bgr;
)";
const char* vertexSource = R"(
#version 410 core
in vec3 inP;
in vec2 inUV;
out vec2 UV;
void main()
gl_Position = vec4(inP, 1.0);
UV = inUV;
)";
vertexShader_ = CompileVertexShader(vertexSource);
fragmentShader_ = CompileFragmentShader(fragmentSource);
programID_ = LinkShaderProgram(vertexShader_, fragmentShader_);
return 0;
extern "C" __declspec(dllexport) void OpenGLKill()
wglDeleteContext(hglrc_);
extern "C" __declspec(dllexport) void OpenGLDraw(void* hdc, float rotation)
HDC validHDC = static_cast<HDC>(hdc);
glClearColor(0.2f, 0.2f, 0.2f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
gl_->glUseProgram(programID_);
gl_->glBindVertexArray(vao_);
gl_->glBindBuffer(GL_ARRAY_BUFFER, uvs_);
gl_->glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexes_);
// Assign the texture...
gl_->glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, calibrationTexture_);
SetUniform("quadTexture", calibrationTexture_);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
gl_->glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, NULL);
gl_->glBindVertexArray(NULL);
gl_->glUseProgram(NULL);
SwapBuffers(validHDC);
extern "C" __declspec(dllexport) void OpenGLResize(int width, int height)
glViewport(0, 0, width, height);
//glMatrixMode(GL_PROJECTION);
//glLoadIdentity();
//glOrtho(width / static_cast<float>(height), -width / static_cast<float>(height), -1.0f, 1.0f, 0.1f, 100.0f);
包含 wpf 客户端的完整代码：https://github.com/spiroyster/wpfogl （分支“GL4”）。
如前所述，我必须在绘制例程期间绑定纹理之前显式调用gl_->glActiveTexture(GL_TEXTURE1)，即使在此之前我从未设置过活动纹理单元（并且在上下文中只加载了一个纹理）。如果我删除该行，即活动纹理单元保留为GL_TEXTURE0，它不会显示纹理。
然后对于我加载的所有后续纹理...即必须将活动纹理单元设置为GL_TEXTURE2，如果它是我在此实例/上下文期间加载的第二个纹理...即使即使我只使用所说的纹理。即即使我只使用第二个纹理进行绘制（而不是第一个加载的纹理），我仍然必须将活动纹理单元显式设置为GL_TEXTURE2。
【问题讨论】：
向我们展示您演示问题的代码，最好简化为minimal reproducible example。 @HolyBlackCat：同意。另见：***.com/questions/8866904/… 好的，谢谢，我会尽快整理一个孤立的例子。 @HolyBlackCat 代码示例已添加。 @Acorn 感谢您的建议，遗憾的是在这种情况下没有添加任何内容。干杯 【参考方案1】：您必须为纹理采样器统一设置的值是纹理单元的索引，而不是纹理对象。
像这样更改您的代码：
gl_->glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, calibrationTexture_);
// this is wrong
//SetUniform("quadTexture", calibrationTexture_);
SetUniform( "quadTexture", 1 ); // 1 because of GL_TEXTURE1
见OpenGL 4.6 API Compatibility Profile Specification; 7.10 Samplers; page 154：
采样器是 OpenGL 着色语言中用于识别的特殊制服 用于每个纹理查找的纹理对象。采样器的值表示正在访问的纹理图像单元。将采样器的值设置为
i选择纹理图像单元号i。
注意，纹理对象的“名称”由
生成glGenTextures(1, &calibrationTexture_);
此“名称”（整数）取决于硬件和驱动程序。 但是由于您的代码中只生成了 1 个纹理对象，因此名称的值很有可能是 1。
这意味着，当你设置
gl_->glActiveTexture(GL_TEXTURE1);
您的代码有效，因为 calibrationTexture_ 的值为 1。
【讨论】：
是的，这解决了它（并且有意义），非常感谢。并感谢您链接 4.6 文档。以上是关于glActiveTexture 默认行为与预期不符的主要内容，如果未能解决你的问题，请参考以下文章