C语言 纹理映射到在 OpenGL 中使用 GL_QUAD_STRIP 制作的圆柱体

Question

所以我在openGL中有一个圆柱体，我没有使用gluCylinder而是使用分段GL_QUAD_STRIP来创建它，以给人一种圆形管的印象。我想得到一个纹理图像来一直包裹在圆柱体周围，但不知道如何;在OpenGL中的纹理方面，我仍然是一个新手，所以也许我不像我想象的那样理解纹理。这是我拥有的代码，用于绘制圆柱体并尝试对其进行纹理处理：

float x,z,angle;            // Used to calculate cylinder wall
float height = 75.0f;       // Height of the cylinder
float diameter = 10.0f;     // Diameter of the cylinder, or more specifically, 
float normal[3],corners[2][3];  // Storeage for vertex calculations
float numSides = 100.0f;
float step;
float sideLength;
float perimeter;            // Not perimeter of ideal circular cylinder
                            // but actual perimeter of what is drawn
int whichSide;              // Used to keep track of which side you are on during the loop
step = (GL_PI/numSides/2.0f);   // Approximate the cylinder wall with
                                // some number of flat segments
sideLength = 
    2.0f*diameter*(float)sin(GL_PI/(2.0f*numSides)); // Calculate the length of each side
perimeter = numSides * sideLength;
printf("There are %f sides on the small cylindernthat are each %f units
     long.nThe dimensions of the texture must benclose to %f x %fnnn", numSides,
     sideLength, perimeter, height);

// Set material color for head of screw
glColor3f(1.0f, 1.0f, 1.0f);
// Assemble the wall as 100 quadrilaterals formed by
// placing adjoining Quads together
glFrontFace(GL_CCW);
glBegin(GL_QUAD_STRIP);

for(angle = (2.0f*GL_PI); angle > 0.0f; angle -= step)
{
    // Calculate x and y position of the first vertex
    x = diameter*(float)sin(angle);
    z = diameter*(float)cos(angle);
    // Get the coordinate for this point and extrude the 
    // length of the cylinder.
    corners[0][0] = x;
    corners[0][1] = -height/2.0f;
    corners[0][2] = z;
    corners[1][0] = x;
    corners[1][1] = height/2.0f;
    corners[1][2] = z;
    // Instead of using real normal to actual flat section
    // Use what the normal would be if the surface was really
    // curved. Since the cylinder goes up the Y axis, the normal 
    // points from the Y axis out directly through each vertex. 
    // Therefore we can use the vertex as the normal, as long as
    // we reduce it to unit length first and assume the y component 
    // to be zero
    normal[0] = corners[1][0];
    normal[1] = 0.0f;
    normal[2] = corners[1][2];


//@@@@@#####*****TEXTURING DONE HERE *****#####@@@@@//
    // Reduce to length of one and specify for this point
    ReduceToUnit(normal);
    glNormal3fv(normal);
    glTexCoord2f(((float)whichSide)/numSides,0.0f);
    glVertex3fv(corners[0]);
    glTexCoord2f(((float)whichSide)/numSides,1.0f);
    glVertex3fv(corners[1]);
    whichSide++;
}

Answer 1

如果您将纹理映射过程视为将一张纸包裹在圆柱体周围（因此圆柱体的高度 = 纸张的高度和圆柱体的周长 = 纸张的宽度），您需要做的就是生成改变 Y（或 X）以及角度的 texcoord（但这将从 0-1 变为 Angle，而角度从 0 变为 Pi）。另一个纹理坐标 X（或 Y）将为 0 和 1，因此它映射到该轴上的全图范围。