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Improve flat stroke for sharp corners with a smooth transition to miter joints

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This commit is contained in:
Grant Sanderson 2024-08-07 10:34:47 -05:00
parent edb438e5e2
commit 61a2b4d0da
1 changed files with 26 additions and 21 deletions
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47
manimlib/shaders/quadratic_bezier_stroke/geom.glsl
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@ -28,11 +28,10 @@ const int MITER_JOINT = 3;
// When the cosine of the angle between
// two vectors is larger than this, we
// consider them aligned
const float COS_THRESHOLD = 0.99;
const float COS_THRESHOLD = 0.999;
// Used to determine how many lines to break the curve into
const float POLYLINE_FACTOR = 30;
const int MAX_STEPS = 32;
const float MITER_LIMIT = 5.0;
#INSERT emit_gl_Position.glsl
#INSERT finalize_color.glsl
@ -50,6 +49,13 @@ vec3 get_joint_unit_normal(vec4 joint_product){
}
vec4 unit_joint_product(vec4 joint_product){
float tol = 1e-8;
float norm = length(joint_product);
return (norm < tol) ? vec4(0.0, 0.0, 0.0, 1.0) : joint_product / norm;
}
vec3 point_on_quadratic(float t, vec3 c0, vec3 c1, vec3 c2){
return c0 + c1 * t + c2 * t * t;
}
@ -86,36 +92,34 @@ vec3 step_to_corner(vec3 point, vec3 tangent, vec3 unit_normal, vec4 joint_produ
so as to make a joint.
*/
vec3 unit_tan = normalize(flat_stroke == 0.0 ? project(tangent, unit_normal) : tangent);
vec4 unit_jp = unit_joint_product(joint_product);
float cos_angle = unit_jp.w;
// Step to stroke width bound should be perpendicular
// both to the tangent and the normal direction
vec3 step = normalize(cross(unit_normal, unit_tan));
// Check if we can avoid creating a joint
if (inner_joint || int(joint_type) == NO_JOINT) return step;
// Conditions where no joint needs to be created
if (inner_joint || int(joint_type) == NO_JOINT || cos_angle > COS_THRESHOLD) return step;
// Find the angle between
if (flat_stroke == 0){
// Figure out what joint product would be for everything projected onto
// the plane perpendicular to the normal direction (which here would be to_camera)
vec3 adj_tan = inverse_vector_product(tangent, joint_product.xyz, joint_product.w);
vec3 adj_tan = inverse_vector_product(tangent, unit_jp.xyz, unit_jp.w);
adj_tan = project(adj_tan, unit_normal);
joint_product = get_joint_product(unit_tan, adj_tan);
vec4 flat_jp = get_joint_product(unit_tan, adj_tan);
cos_angle = unit_joint_product(flat_jp).w;
}
float cos_angle = (length(joint_product) > 1e-10) ? normalize(joint_product).w : 1.0;
if(cos_angle > 1 - 1e-3) return step;
// Adjust based on the joint.
// Bevel for cos(angle) > -0.7, smoothly transition
// to miter for those with sharper angles
float sin_angle = sqrt(1 - cos_angle * cos_angle) * sign(dot(joint_product.xyz, unit_normal));
float miter_factor = (int(joint_type) == MITER_JOINT) ?
1.0 : smoothstep(-0.7, -0.9, cos_angle);
float shift = (cos_angle + mix(-1, 1, miter_factor)) / sin_angle;
// Adjust based on the joint
float shift = (int(joint_type) == MITER_JOINT) ?
(cos_angle + 1.0) / sin_angle :
(cos_angle - 1.0) / sin_angle;
step = step + shift * unit_tan;
if (length(step) > MITER_LIMIT){
step = MITER_LIMIT * normalize(step);
}
return step;
return step + shift * unit_tan;
}
@ -155,6 +159,7 @@ void emit_point_with_width(
color = finalize_color(joint_color, point, unit_normal);
if (width == 0) scaled_anti_alias_width = -1.0; // Signal to discard in the frag shader
else scaled_anti_alias_width = 2.0 * anti_alias_width * pixel_size / width;
width += anti_alias_width * pixel_size;
// Emit two corners
// The frag shader will receive a value from -1 to 1,