c++ - glGenTextures 有效但每次都返回相同的纹理名称

Question

我有一个名为 Texture 的类。此类负责管理纹理。在程序启动中，OpenGL 上下文被正确初始化(这就是使这个问题不同于大多数涉及意外 glGenTextures 行为的问题)。 Texture 从 glGenTextures() 获取纹理名称，然后通过函数 texGLInit() 将图像数据加载并绑定(bind)到该纹理名称的内存中。 这有效，并且纹理显示完全符合预期。

但是，我还希望我的纹理能够更改它在用户单击按钮并从 OpenFileDiaglog 中的 HDD 中选择一个时显示的纹理。此函数称为 reloadTexture()。此函数尝试从内存中删除旧图像/像素数据，并用用户选择的文件中的新数据替换它。 然而，当发生这种情况时，它会使用 glDeleteTextures 删除纹理名称，然后分配一个新的纹理名称并使用函数 texGLInit() 将新像素数据加载到内存中。但是纹理名称在 100% 的情况下与之前的名称(通常为“1”)完全相同。

发生这种情况后显示的图像很奇怪。它具有新的图像尺寸，但仍然是旧图像的像素。简而言之，它将旧图像扭曲到新图像的大小。它仍在使用据称已删除的像素数据进行绘制。应该发生的是屏幕现在在屏幕上显示新的图像文件。我相信这与纹理名称不唯一有关。

代码如下:

Texture::Texture(string filename)//---Constructor loads in the initial image. Works fine!
{
    textureID[0]=0;

    const char* fnPtr = filename.c_str(); //our image loader accepts a ptr to a char, not a string
    //printf(fnPtr);

    lodepng::load_file(buffer, fnPtr);//load the file into a buffer

    unsigned error = lodepng::decode(image,w,h,buffer);//lodepng's decode function will load the pixel data into image vector from the buffer
    //display any errors with the texture
    if(error)
    {
        cout << "\ndecoder error " << error << ": " << lodepng_error_text(error) <<endl;
    }
    //execute the code that'll throw exceptions to do with the images size
    checkPOT(w);
    checkPOT(h);


    //image now contains our pixeldata. All ready for OpenGL to do its thing

    //let's get this texture up in the video memory
    texGLInit();

    Draw_From_Corner = CENTER;  
}

void Texture::reloadTexture(string filename)//Reload texture replaces the texture name and image/pixel data bound to this texture
{
    //first and foremost clear the image and buffer vectors back down to nothing so we can start afresh 
    buffer.clear();
    image.clear();
    w = 0;
    h = 0;
    //also delete the texture name we were using before
    glDeleteTextures(1, &textureID[0]);




    const char* fnPtr = filename.c_str(); //our image loader accepts a ptr to a char, not a string
    //printf(fnPtr);

    lodepng::load_file(buffer, fnPtr);//load the file into a buffer

    unsigned error = lodepng::decode(image,w,h,buffer);//lodepng's decode function will load the pixel data into image vector from the buffer
    //display any errors with the texture
    if(error)
    {
        cout << "\ndecoder error " << error << ": " << lodepng_error_text(error) <<endl;
    }
    //execute the code that'll throw exceptions to do with the images size
    checkPOT(w);
    checkPOT(h);

    //image now contains our pixeldata. All ready for  to do its thing

    //let's get this texture up in the video memoryOpenGL
    texGLInit();

    Draw_From_Corner = CENTER;
}

void Texture::texGLInit()//Actually gets the new texture name loads the pixeldata into openGL
{
    glGenTextures(1, &textureID[0]);
    ////printf("\ntextureID = %u", textureID[0]);
    glBindTexture(GL_TEXTURE_2D, textureID[0]);//evrything we're about to do is about this texture
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
    //glDisable(GL_COLOR_MATERIAL);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8,w,h,0, GL_RGBA, GL_UNSIGNED_BYTE, &image[0]);
    //we COULD free the image vectors memory right about now. But we'll do it when there's a need to. At the beginning of the reloadtexture func, makes sure it happens when we need it to.



}

这里值得一提的是 Texture 类中的绘制函数。

void Texture::draw(point* origin, ANCHOR drawFrom)
{
    //let us set the DFC enum here.
    Draw_From_Corner = drawFrom;

    glEnable(GL_TEXTURE_2D);
    //printf("\nDrawing texture at (%f, %f)",centerPoint.x, centerPoint.y);
    glBindTexture(GL_TEXTURE_2D, textureID[0]);//bind the texture
    //create a quick vertex array for the primitive we're going to bind the texture to
    ////printf("TexID = %u",textureID[0]);
    GLfloat vArray[8];

#pragma region anchor switch
    switch (Draw_From_Corner)
    {
    case CENTER:

        vArray[0] = origin->x-(w/2); vArray[1] = origin->y-(h/2);//bottom left i0
        vArray[2] = origin->x-(w/2); vArray[3] = origin->y+(h/2);//top left i1
        vArray[4] = origin->x+(w/2); vArray[5] = origin->y+(h/2);//top right i2
        vArray[6] = origin->x+(w/2); vArray[7] = origin->y-(h/2);//bottom right i3
        break;

    case BOTTOMLEFT:

        vArray[0] = origin->x; vArray[1] = origin->y;//bottom left i0
        vArray[2] = origin->x; vArray[3] = origin->y+h;//top left i1
        vArray[4] = origin->x+w; vArray[5] = origin->y+h;//top right i2
        vArray[6] = origin->x+w; vArray[7] = origin->y;//bottom right i3

        break;

    case TOPLEFT:

        vArray[0] = origin->x; vArray[1] = origin->y-h;//bottom left i0
        vArray[2] = origin->x; vArray[3] = origin->y;//top left i1
        vArray[4] = origin->x+w; vArray[5] = origin->y;//top right i2
        vArray[6] = origin->x+w; vArray[7] = origin->y-h;//bottom right i3

        break;

    case TOPRIGHT:

        vArray[0] = origin->x-w; vArray[1] = origin->y-h;//bottom left i0
        vArray[2] = origin->x-w; vArray[3] = origin->y;//top left i1
        vArray[4] = origin->x; vArray[5] = origin->y;//top right i2
        vArray[6] = origin->x; vArray[7] = origin->y-h;//bottom right i3

        break;

    case BOTTOMRIGHT:

        vArray[0] = origin->x-w; vArray[1] = origin->y;//bottom left i0
        vArray[2] = origin->x-w; vArray[3] = origin->y+h;//top left i1
        vArray[4] = origin->x-h; vArray[5] = origin->y;//top right i2
        vArray[6] = origin->x; vArray[7] = origin->y;//bottom right i3

        break;

    default: //same as center

        vArray[0] = origin->x-(w/2); vArray[1] = origin->y-(h/2);//bottom left i0
        vArray[2] = origin->x-(w/2); vArray[3] = origin->y+(h/2);//top left i1
        vArray[4] = origin->x+(w/2); vArray[5] = origin->y+(h/2);//top right i2
        vArray[6] = origin->x+(w/2); vArray[7] = origin->y-(h/2);//bottom right i3

        break;


    }
#pragma  endregion          

    //create a quick texture array (we COULD create this on the heap rather than creating/destoying every cycle)
    GLfloat tArray[8] = 
    {
        //this has been tinkered with from my normal order. I think LodePNG is bringing the PD upside down. SO A QUICK FIX HERE WAS NECESSARY.
        0.0f,1.0f,//0
        0.0f,0.0f,//1
        1.0f,0.0f,//2
        1.0f,1.0f//3
    };

    //and finally.. the index array...remember, we draw in triangles....(and we'll go CW)
    GLubyte iArray[6] =
    {
        0,1,2,
        0,2,3
    };

    //Activate arrays
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);

    //Give openGL a pointer to our vArray and tArray
    glVertexPointer(2, GL_FLOAT, 0, &vArray[0]);
    glTexCoordPointer(2, GL_FLOAT, 0, &tArray[0]);

    //Draw it all
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_BYTE, &iArray[0]);

    //glDrawArrays(GL_TRIANGLES,0,6);

    //Disable the vertex arrays
    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
    glDisable(GL_TEXTURE_2D);
}

谁能告诉我为什么 OpenGL 不会加载我加载到其中的新像素数据并从中绘制？正如我所说，我怀疑这与 glGenTextures 没有给我新的纹理名称有关。

Answer 1

您正在调用 glTexImage2D 并将指针传递给客户端内存。当心，文档说:

If a non-zero named buffer object is bound to the GL_PIXEL_UNPACK_BUFFER target (see glBindBuffer) while a texture image is specified, data is treated as a byte offset into the buffer object's data store.

为了安全起见，您可能希望调用 glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0) 解除绑定(bind)任何缓冲区对象。