如何在 opengl 中跨多个四边形平滑纹理

Question

我正在尝试使用我找到并调整大小的木头位图为木头模型 table 制作纹理，但是我遇到的问题是每个四边形构成了 table 在应用纹理时清晰可见。我如何让它看起来像一个光滑的纹理？

void Table::DrawTableTop()
{
    glPushMatrix();
    //draw tabletop

    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, texid);

    glBegin(GL_QUADS);
    glMaterialfv(GL_FRONT, GL_SPECULAR, static_cast<GLfloat*>(specular));
    glMaterialf(GL_FRONT, GL_SHININESS, static_cast<GLfloat>(shininess));

    float unitx = 1.0f / (float)(xsize * 2 + 1);
    float unity = 1.0f / (float)(zsize * 2 + 1);

    for (int i = -xsize; i <= xsize; i++)
    {
        for (int j = -zsize; j <= zsize; j++)
        {
            glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, static_cast<GLfloat*>(wDiffuse));
            //top
            glNormal3f(0.0f, 1.0f, 0.0f);
            if (tex) glTexCoord2f(unitx * static_cast<float>(i + 20 + 1), unity * static_cast<float>(j + 10));
            glVertex3f(scale[0] * static_cast<float>(i) + scale[0], 0, scale[2] * static_cast<float>(j) + scale[2]);
            if (tex) glTexCoord2f(unitx * static_cast<float>(i + 20 + 1), unity * static_cast<float>(j + 10 + 1));
            glVertex3f(scale[0] * static_cast<float>(i) + scale[0], 0, scale[2] * static_cast<float>(j));
            if (tex) glTexCoord2f(unitx * static_cast<float>(i + 20), unity * static_cast<float>(j + 10 + 1));
            glVertex3f(scale[0] * static_cast<float>(i), 0, scale[2] * static_cast<float>(j));
            if (tex) glTexCoord2f(unitx * static_cast<float>(i + 20 ), unity * static_cast<float>(j + 10));
            glVertex3f(scale[0] * static_cast<float>(i), 0, scale[2] * static_cast<float>(j) + scale[2]);
        }
    }

    glEnd();

    glBindTexture(GL_TEXTURE_2D, 0);
    glDisable(GL_TEXTURE_2D);

    glPopMatrix();

xsize和zsize的值分别是20和10

我希望纹理看起来像是加载到一个大四边形上，但显然使用多个四边形来改善照明等。

纹理图像是这样的：

Answer 1

你弄乱了第二个纹理坐标。当顶点位置有+ scale[0]时设置为j + 20，当顶点位置没有+ scale[0]时设置为j + 20 + 1。结果你所有的条带都是 'inverted'.

要修复它，请使用：

if (tex) glTexCoord2f(unitx * static_cast<float>(i + 20 + 1), unity * static_cast<float>(j + 10 + 1));
glVertex3f(scale[0] * static_cast<float>(i) + scale[0], 0, scale[2] * static_cast<float>(j) + scale[2]);
if (tex) glTexCoord2f(unitx * static_cast<float>(i + 20 + 1), unity * static_cast<float>(j + 10));
glVertex3f(scale[0] * static_cast<float>(i) + scale[0], 0, scale[2] * static_cast<float>(j));
if (tex) glTexCoord2f(unitx * static_cast<float>(i + 20), unity * static_cast<float>(j + 10));
glVertex3f(scale[0] * static_cast<float>(i), 0, scale[2] * static_cast<float>(j));
if (tex) glTexCoord2f(unitx * static_cast<float>(i + 20 ), unity * static_cast<float>(j + 10 + 1));
glVertex3f(scale[0] * static_cast<float>(i), 0, scale[2] * static_cast<float>(j) + scale[2]);

不过，更好的方法，是提取顶点位置计算如下：

struct Vertex {
    float texcoord[2];
    float position[3];
};

Vertex vertex_at(float scale[3], float unitx, float unity, int i, int j)
{
    Vertex ret;
    ret.texcoord[0] = unitx*(i + 20);
    ret.texcoord[1] = unity*(j + 10);
    ret.position[0] = scale[0]*i;
    ret.position[1] = 0;
    ret.position[2] = scale[2]*j;
    return ret;
}

然后像这样使用它：

for (int i = -xsize; i <= xsize; i++)
{
    for (int j = -zsize; j <= zsize; j++)
    {
        glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, static_cast<GLfloat*>(wDiffuse));
        //top
        glNormal3f(0.0f, 1.0f, 0.0f);
        Vertex v[4] = {
            vertex_at(scale, unitx, unity, i + 1, j + 1),
            vertex_at(scale, unitx, unity, i + 1, j),
            vertex_at(scale, unitx, unity, i, j),
            vertex_at(scale, unitx, unity, i, j + 1),
        };
        for(int k = 0; k < 4; ++k) {
            if (tex) glTexCoord2fv(v[k].texcoord);
            glVertex3fv(v[k].position);
        }
    }
}

这样可以更轻松地了解正在发生的事情，并且您离使用 VAO 更近了一步：只需将所有这些 Vertex 结构捆绑到一个缓冲区中并设置属性指针。

Answer 2

瓷砖上的纹理沿 y 轴翻转。更改纹理坐标：

if (tex) 
    glTexCoord2f(
        unitx * static_cast<float>(i + 20 + 1),
        unity * static_cast<float>(j + 10 + 1));
glVertex3f(scale[0] * static_cast<float>(i) + scale[0], 0, scale[2] * static_cast<float>(j) + scale[2]);

if (tex) 
    glTexCoord2f(
        unitx * static_cast<float>(i + 20 + 1),
        unity * static_cast<float>(j + 10));
glVertex3f(scale[0] * static_cast<float>(i) + scale[0], 0, scale[2] * static_cast<float>(j));

if (tex)
    glTexCoord2f(
        unitx * static_cast<float>(i + 20),
        unity * static_cast<float>(j + 10));
glVertex3f(scale[0] * static_cast<float>(i), 0, scale[2] * static_cast<float>(j));

if (tex)
    glTexCoord2f(
        unitx * static_cast<float>(i + 20 ),
        unity * static_cast<float>(j + 10 + 1));
glVertex3f(scale[0] * static_cast<float>(i), 0, scale[2] * static_cast<float>(j) + scale[2]);

如何在 opengl 中跨多个四边形平滑纹理

How to smooth texture across multiple quads in opengl

c++

opengl

textures

opengl-compat