c - 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，我不是使用 gluCylinder 创建的，而是使用分段的 GL_QUAD_STRIP 来给人一种圆管的印象。我想得到一个纹理图像来环绕圆柱体，但不知道如何；当涉及到 OpenGL 中的纹理时，我仍然是一个新手，所以也许我不像我想的那样理解纹理。这是我绘制圆柱体并尝试对其进行纹理化的代码:

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 cylinder\nthat are each %f units
     long.\nThe dimensions of the texture must be\nclose to %f x %f\n\n\n", 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想象成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，圆柱体的周长 = 纸张的宽度)，您需要做的就是生成随角度改变 Y(或 X)的纹理坐标(但这将从 0-1 变化，而角度从 0 变化到 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完整范围。