83 lines
2.4 KiB
GLSL
83 lines
2.4 KiB
GLSL
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uniform mat4 ViewMatrix;
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uniform mat4 ProjectionMatrix;
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/* ---- Instantiated Attribs ---- */
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in vec2 pos;
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/* ---- Per instance Attribs ---- */
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in mat4 InstanceModelMatrix;
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in vec3 stateColor;
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in vec3 boneColor;
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flat out vec3 finalStateColor;
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flat out vec3 finalBoneColor;
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flat out mat4 sphereMatrix;
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out vec3 viewPosition;
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/* Sphere radius */
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const float rad = 0.05;
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void main()
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{
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mat4 model_view_matrix = ViewMatrix * InstanceModelMatrix;
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sphereMatrix = inverse(model_view_matrix);
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bool is_persp = (ProjectionMatrix[3][3] == 0.0);
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/* This is the local space camera ray (not normalize).
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* In perspective mode it's also the viewspace position
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* of the sphere center. */
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vec3 cam_ray = (is_persp) ? model_view_matrix[3].xyz : vec3(0.0, 0.0, -1.0);
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cam_ray = mat3(sphereMatrix) * cam_ray;
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/* Sphere center distance from the camera (persp) in local space. */
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float cam_dist = length(cam_ray);
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/* Compute view aligned orthonormal space. */
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vec3 z_axis = cam_ray / cam_dist;
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vec3 x_axis = normalize(cross(sphereMatrix[1].xyz, z_axis));
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vec3 y_axis = cross(z_axis, x_axis);
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float z_ofs = -rad - 1e-8; /* offset to the front of the sphere */
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if (is_persp) {
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/* For perspective, the projected sphere radius
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* can be bigger than the center disc. Compute the
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* max angular size and compensate by sliding the disc
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* towards the camera and scale it accordingly. */
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const float half_pi = 3.1415926 * 0.5;
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/* Let be (in local space):
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* V the view vector origin.
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* O the sphere origin.
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* T the point on the target circle.
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* We compute the angle between (OV) and (OT). */
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float a = half_pi - asin(rad / cam_dist);
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float cos_b = cos(a);
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float sin_b = sqrt(clamp(1.0 - cos_b * cos_b, 0.0, 1.0));
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#if 1
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/* Instead of choosing the biggest circle in screenspace,
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* we choose the nearest with the same angular size. This
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* permit us to leverage GL_ARB_conservative_depth in the
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* fragment shader. */
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float minor = cam_dist - rad;
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float major = cam_dist - cos_b * rad;
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float fac = minor / major;
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sin_b *= fac;
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#else
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z_ofs = -rad * cos_b;
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#endif
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x_axis *= sin_b;
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y_axis *= sin_b;
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}
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/* Camera oriented position (but still in local space) */
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vec3 cam_pos = x_axis * pos.x + y_axis * pos.y + z_axis * z_ofs;
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vec4 V = model_view_matrix * vec4(cam_pos, 1.0);
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gl_Position = ProjectionMatrix * V;
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viewPosition = V.xyz;
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finalStateColor = stateColor;
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finalBoneColor = boneColor;
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}
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