使用 Qt3D 2.0 的广告牌

Finally, we created custom shaders to draw the billboards. Note that because we were drawing impostor spheres, the billboard size was increased to handle raytracing in the fragment shader from awkward angles. You likely do not need the 2.0*0.6 factor in general.

顶点着色器:

#version 330

in vec3 vertexPosition;
in float vertexId;
in vec3 pos;
in vec3 col;
in float scale;

uniform vec3 eyePosition = vec3(0.0, 0.0, 0.0);

uniform mat4 modelMatrix;
uniform mat4 mvp;

out vec3 modelSpherePosition;
out vec3 modelPosition;
out vec3 color;
out vec2 planePosition;
out float radius;
vec3 makePerpendicular(vec3 v) {
    if(v.x == 0.0 && v.y == 0.0) {
        if(v.z == 0.0) {
            return vec3(0.0, 0.0, 0.0);
        }
        return vec3(0.0, 1.0, 0.0);
    }
    return vec3(-v.y, v.x, 0.0);
}

void main() {
    vec3 position = vertexPosition + pos;
    color = col;
    radius = scale;
    modelSpherePosition = (modelMatrix * vec4(position, 1.0)).xyz;

    vec3 view = normalize(position - eyePosition);
    vec3 right = normalize(makePerpendicular(view));
    vec3 up = cross(right, view);

    float texCoordX = 1.0 - 2.0*(float(vertexId==0.0) + float(vertexId==2.0));
    float texCoordY = 1.0 - 2.0*(float(vertexId==0.0) + float(vertexId==1.0));
    planePosition = vec2(texCoordX, texCoordY);

    position += 2*0.6*(-up - right)*(scale*float(vertexId==0.0));
    position += 2*0.6*(-up + right)*(scale*float(vertexId==1.0));
    position += 2*0.6*(up - right)*(scale*float(vertexId==2.0));
    position += 2*0.6*(up + right)*(scale*float(vertexId==3.0));

    vec4 modelPositionTmp = modelMatrix * vec4(position, 1.0);
    modelPosition = modelPositionTmp.xyz;

    gl_Position = mvp*vec4(position, 1.0);
}

片段着色器:

#version 330

in vec3 modelPosition;
in vec3 modelSpherePosition;
in vec3 color;
in vec2 planePosition;
in float radius;

out vec4 fragColor;

uniform mat4 modelView;
uniform mat4 inverseModelView;
uniform mat4 inverseViewMatrix;
uniform vec3 eyePosition;
uniform vec3 viewVector;

void main(void) {
    vec3 rayDirection = eyePosition - modelPosition;
    vec3 rayOrigin = modelPosition - modelSpherePosition;

    vec3 E = rayOrigin;
    vec3 D = rayDirection;

    // Sphere equation
    //      x^2 + y^2 + z^2 = r^2
    // Ray equation is
    //     P(t) = E + t*D
    // We substitute ray into sphere equation to get
    //     (Ex + Dx * t)^2 + (Ey + Dy * t)^2 + (Ez + Dz * t)^2 = r^2
    float r2 = radius*radius;
    float a = D.x*D.x + D.y*D.y + D.z*D.z;
    float b = 2.0*E.x*D.x + 2.0*E.y*D.y + 2.0*E.z*D.z;
    float c = E.x*E.x + E.y*E.y + E.z*E.z - r2;

    // discriminant of sphere equation
    float d = b*b - 4.0*a*c;
    if(d < 0.0) {
        discard;
    }

    float t = (-b + sqrt(d))/(2.0*a);
    vec3 sphereIntersection = rayOrigin + t * rayDirection;

    vec3 normal = normalize(sphereIntersection);
    vec3 normalDotCamera = color*dot(normal, normalize(rayDirection));

    float pi = 3.1415926535897932384626433832795;

    vec3 position = modelSpherePosition + sphereIntersection;

    // flat red
    fragColor = vec4(1.0, 0.0, 0.0, 1.0);
}

自从我们第一次实现它以来已经有一段时间了，现在可能有更简单的方法来实现它，但这应该让你对你需要的部分有所了解.