多紋理問題

Question

我想通過在固定的 管線中使用多紋理特徵來混合多達4個紋理。我可以成功地使用2個紋理單元，但是當我使用多於兩個紋理單元時，出現了奇怪的僞像（某些紋理丟失或紋理座標錯誤 ）。我不知道我做錯了什麼。

的代碼非常簡單：

glGetIntegerv(GL_MAX_TEXTURE_UNITS, &TextureUnits); 
if (TextureUnits > 4) 
    TextureUnits = 4; 

// set textures parameters: texCoords and multitexturing combination 
for (int j = 0; j < TextureUnits; ++j) 
{ 
    glActiveTexture(GL_TEXTURE0 + j); 

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); 
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); 

    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP); 
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP); 

    if (j == 0) 
    { 
     glEnable(GL_TEXTURE_2D); 
     //glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL); 
     glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE); 
    } 
    else 
    { 
     // Interpolate : 
     //  Arg0 * Arg2 + Arg1 * (1 - Arg2) 
     // Set arguments to obtain the fallowing blending equation: 
     //  SRCrgb * SRCalpha + DSTrgb * (1 - SRCalpha) 
     glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE); 
     glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_INTERPOLATE); 
     glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_TEXTURE); 
     glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_PREVIOUS); 
     glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE2_RGB, GL_TEXTURE); 
     glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR); 
     glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR); 
     glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND2_RGB, GL_SRC_ALPHA); 

     glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_INTERPOLATE); 
     glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_ALPHA, GL_TEXTURE); 
     glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_ALPHA, GL_PREVIOUS); 
     glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE2_ALPHA, GL_TEXTURE); 
     glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_ALPHA, GL_SRC_ALPHA); 
     glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_ALPHA, GL_SRC_ALPHA); 
     glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND2_ALPHA, GL_SRC_ALPHA); 
    } 

    glEnableClientState(GL_TEXTURE_COORD_ARRAY); 

    glClientActiveTexture(GL_TEXTURE0 + j); 
    glTexCoordPointer(2, GL_FLOAT, sizeof(Vertex), &Mesh->Vertices[0].TexCoords); 
} 

... 

for (int i = 0; i < TextureUnits; ++i) 
{ 
    glActiveTexture(GL_TEXTURE0 + i); 
    glDisable(GL_TEXTURE_2D); 
} 

// use multitexturing and mulipasses when there are needed. 
count = ; // number of textures to blend It could be from 1 to 4. 
do 
{ 
    tex = 0; 
    while (index < count && tex != TextureUnits) 
    {   
     texture = textures[index]; 

     glActiveTexture(GL_TEXTURE0 + tex);   
     glEnable(GL_TEXTURE_2D); 

     setTextureMatrix(texture); 

     glBindTexture(GL_TEXTURE_2D, texture->getGLTexture()); 

     index++; 
     tex++; 
    } 

    if (tex < TextureUnits) 
    { 
     glActiveTexture(GL_TEXTURE0 + tex); 
     glDisable(GL_TEXTURE_2D); 
    } 

    glDrawElements(...); 

} while (index < count); 

Answer 1

在此之後：

glGetIntegerv(GL_MAX_TEXTURE_UNITS, &TextureUnits); 

是什麼TextureUnits的價值？我認爲它是2.