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Remove antialiasing artifacts when drawing lines at a very big scale.

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When drawing lines at scales>1 the inner workings (gradients) of the
antialiasing too were upscaled and became visible. When the scale was very
large this produced interesing yet unexpected visuals.
This commit is contained in:
vrld
2012-05-09 17:17:16 +02:00
parent 4a04c48891
commit b5f3addd35
1 changed files with 16 additions and 10 deletions
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src/modules/graphics/opengl/Graphics.cpp
+16 -10
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@@ -755,7 +755,7 @@ namespace opengl
//
// The intersection points can be calculated using cramers rule.
static void pushIntersectionPoints(Vector *vertices, Vector* overdraw,
int pos, int count, float hw, float inv_hw,
int pos, int count, float hw, float overdraw_factor,
const Vector& p, const Vector& q, const Vector& r)
{
// calculate line directions
@@ -794,8 +794,8 @@ namespace opengl
if (overdraw)
{
// displacement of the overdraw vertices (works by magic).
Vector x = (vertices[pos] - q) * inv_hw;
// displacement of the overdraw vertices
Vector x = (vertices[pos] - q) * overdraw_factor;
overdraw[pos] = vertices[pos];
overdraw[pos+1] = vertices[pos] + x;
@@ -871,14 +871,20 @@ namespace opengl
Vector p,q,r;
bool looping = (coords[0] == coords[count-2]) && (coords[1] == coords[count-1]);
float halfwidth = lineWidth/2.f;
float inv_hw = 1.f / halfwidth;
float halfwidth = lineWidth/2.f;
float overdraw_factor = .0f;
if (lineStyle == LINE_SMOOTH) {
overdraw = new Vector[2*count+2];
// Overdraw changes visible line width. account for that.
// Value of 0.2 chosen empirically.
halfwidth -= .2f;
// TODO: is there a better way to get the pixel size at the current scale?
GLfloat m[16];
glGetFloatv(GL_MODELVIEW_MATRIX, m);
float det = m[0]*m[5]*m[10] + m[4]*m[9]*m[2] + m[8]*m[1]*m[6];
det -= m[2]*m[5]*m[8] + m[6]*m[9]*m[0] + m[10]*m[1]*m[4];
float pixel_size = 1. / sqrt(det);
overdraw_factor = pixel_size / halfwidth;
halfwidth = std::max(.0f, halfwidth - .25f*pixel_size);
}
// get line vertex boundaries
@@ -893,7 +899,7 @@ namespace opengl
{
p = q; q = r;
r = Vector(coords[i+2], coords[i+3]);
pushIntersectionPoints(vertices, overdraw, i, count, halfwidth, inv_hw, p,q,r);
pushIntersectionPoints(vertices, overdraw, i, count, halfwidth, overdraw_factor, p,q,r);
}
// if not looping, extend the line at the end, else use first point as `r'
@@ -902,7 +908,7 @@ namespace opengl
r += q - p;
else
r = Vector(coords[2], coords[3]);
pushIntersectionPoints(vertices, overdraw, count-2, count, halfwidth, inv_hw, p,q,r);
pushIntersectionPoints(vertices, overdraw, count-2, count, halfwidth, overdraw_factor, p,q,r);
// end get line vertex boundaries
// draw the core line