ios - 用 GL_TRIANGLE_STRIP 绘制圆弧

Question

我正在尝试编写一种方法，使用 GL_TRIANGLE_STRIP 绘制从起始角到结束角的弧。我编写了以下代码，但存在以下问题:

1. 我似乎无法找到合适的角度。它们似乎偏离了应有的位置(不是 90/45/180)。
2. 如果两者之间的总角度大于 180 度，则圆弧将在两者之间的圆上绘制较小的角度。即，如果总角度为 200 度，它将在圆的另一部分绘制一个 160 度的弧。

我花了很多时间试图解决这个问题，并认为让另一双眼睛审视我的代码会很有帮助。下图显示了我试图在角度之间创建的三角形 strip 。弄清楚这部分后，我将应用纹理。感谢您的帮助!

-(void) drawArcFrom:(CGFloat)startAngle to:(CGFloat)endAngle position:(CGFloat)position radius:(CGPoint)radius {

    CGFloat segmentWidth = 10.0;
    CGFloat increment = fabsf(endAngle - startAngle) / segmentWidth;
    int numSegs = fabsf(endAngle - startAngle) / segmentWidth;
    int direction = (endAngle - startAngle > 0) ? 1 : -1;

    ccVertex2F vertices[numSegs * 2];

    for (int i = 0; i < numSegs; i++) {
        CGFloat angle = startAngle - (i * increment * direction);
        CGPoint outsidePoint = ccpAdd(position, ccp(sinf(CC_DEGREES_TO_RADIANS(angle)) * (radius + 4), cosf(CC_DEGREES_TO_RADIANS(angle)) * (radius + 4)));
        CGPoint insidePoint = ccpAdd(position, ccp(sinf(CC_DEGREES_TO_RADIANS(angle)) * (radius - 4), cosf(CC_DEGREES_TO_RADIANS(angle)) * (radius - 4)));

        vertices[i * 2] = (ccVertex2F) {outsidePoint.x, outsidePoint.y };
        vertices[i * 2 + 1] = (ccVertex2F) {insidePoint.x, insidePoint.y };
    }

    glVertexPointer(2, GL_FLOAT, 0, vertices);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, (GLsizei) numSegs * 2);

}

Answer 1

我的 android 代码用于整圈。段 = 20；坐标 [x,y,z]

    float w2 = width / 2f;
    float h2 = height / 2f;

    double radius = Math.min(w2, h2);
    double PI2 = Math.PI * 2d;
    coords = new float[SEGMENTS * 2 * 3];
    double angle;
    int index = 0;
    double min_radius = radius - circle_width;
    double max_radius = radius + circle_width;
    for (int i = 0; i < SEGMENTS; i++, index += 6) {
        angle = (PI2 * (double) i) / (double) (SEGMENTS - 1);
        double sin_angle = Math.sin(angle);
        double cos_angle = Math.cos(angle);
        coords[index + 0] = (float) (cos_angle * max_radius);
        coords[index + 1] = (float) (sin_angle * max_radius);
        coords[index + 2] = 0f;
        coords[index + 3] = (float) (cos_angle * min_radius);
        coords[index + 4] = (float) (sin_angle * min_radius);
        coords[index + 5] = 0f;
    }