1 files changed, 68 insertions, 6 deletions

diff --git a/source/blender/draw/engines/gpencil/shaders/gpencil_point_geom.glsl b/source/blender/draw/engines/gpencil/shaders/gpencil_point_geom.glsl
index 6c22633c521..32aaa057298 100644
--- a/source/blender/draw/engines/gpencil/shaders/gpencil_point_geom.glsl
+++ b/source/blender/draw/engines/gpencil/shaders/gpencil_point_geom.glsl
@@ -1,6 +1,7 @@
 uniform mat4 ModelViewProjectionMatrix;
 uniform vec2 Viewport;
 uniform int xraymode;
+uniform int use_follow_path;
 
 layout(points) in;
 layout(triangle_strip, max_vertices = 4) out;
@@ -8,6 +9,7 @@ layout(triangle_strip, max_vertices = 4) out;
 in vec4 finalColor[1];
 in float finalThickness[1];
 in vec2 finaluvdata[1];
+in vec4 finalprev_pos[1];
 
 out vec4 mColor;
 out vec2 mTexCoord;
@@ -15,6 +17,10 @@ out vec2 mTexCoord;
 #define GP_XRAY_FRONT 0
 #define GP_XRAY_3DSPACE 1
 
+#define M_PI        3.14159265358979323846  /* pi */
+#define M_2PI       6.28318530717958647692  /* 2*pi */
+#define FALSE       0
+
 /* project 3d point to 2d on screen space */
 vec2 toScreenSpace(vec4 vertex)
 {
@@ -45,33 +51,89 @@ vec2 rotateUV(vec2 uv, float angle)
 	return rot_uv + vec2(0.5f, 0.5f);
 }
 
+vec2 rotatePoint(vec2 center, vec2 point, float angle)
+{
+	/* translate center of rotation to the center */
+	vec2 new_point = point - center;
+	vec2 rot_point;
+	rot_point.x = new_point.x * cos(angle) - new_point.y * sin(angle);
+	rot_point.y = new_point.y * cos(angle) + new_point.x * sin(angle);
+	return rot_point + center;
+}
+
+/* Calculate angle of the stroke using previous point as reference.
+ * The angle is calculated using the x axis (1, 0) as 0 degrees */
+float getAngle(vec2 pt0, vec2 pt1)
+{
+	/* do not rotate one point only (no reference to rotate) */
+	if (pt0 == pt1) {
+		return 0.0;
+	}	
+
+	if (use_follow_path == FALSE) {
+		return 0.0;
+	}
+
+	/* default horizontal line (x-axis) in screen space */
+	vec2 v0 = vec2(1.0, 0.0);
+	
+	/* vector of direction */
+	vec2 vn = vec2(normalize(pt1 - pt0));
+	
+	/* angle signed (function ported from angle_signed_v2v2) */
+	float perp_dot = (v0[1] * vn[0]) - (v0[0] * vn[1]);
+	float angle = atan(perp_dot, dot(v0, vn));
+	
+	/* get full circle rotation */
+	if (angle > 0.0) {
+		angle = M_PI + (M_PI - angle);
+	}
+	else {
+		angle *= -1.0;
+	}
+
+	return angle;
+}
+
 void main(void)
 {
-	/* receive 4 points */
+	/* receive points */
 	vec4 P0 = gl_in[0].gl_Position;
 	vec2 sp0 = toScreenSpace(P0);
 
+	vec4 P1 = finalprev_pos[0];
+	vec2 sp1 = toScreenSpace(P1);
+    vec2 point;
+
 	float size = finalThickness[0];
-	float aspect = 1.0;
+	vec2 center = vec2(sp0.x, sp0.y);
+	
+	/* get angle of stroke to rotate texture */
+	float angle = getAngle(sp0, sp1);
+
 	/* generate the triangle strip */
 	mTexCoord = rotateUV(vec2(0, 1), finaluvdata[0].y);
 	mColor = finalColor[0];
-	gl_Position = vec4(vec2(sp0.x - size, sp0.y + size * aspect) / Viewport, getZdepth(P0), 1.0);
+	point = rotatePoint(center, vec2(sp0.x - size, sp0.y + size), angle);
+	gl_Position = vec4(point / Viewport, getZdepth(P0), 1.0);
 	EmitVertex();
 
 	mTexCoord = rotateUV(vec2(0, 0), finaluvdata[0].y);
 	mColor = finalColor[0];
-	gl_Position = vec4(vec2(sp0.x - size, sp0.y - size * aspect) / Viewport, getZdepth(P0), 1.0);
+	point = rotatePoint(center, vec2(sp0.x - size, sp0.y - size), angle);
+	gl_Position = vec4(point / Viewport, getZdepth(P0), 1.0);
 	EmitVertex();
 
 	mTexCoord = rotateUV(vec2(1, 1), finaluvdata[0].y);
 	mColor = finalColor[0];
-	gl_Position = vec4(vec2(sp0.x + size, sp0.y + size * aspect) / Viewport, getZdepth(P0), 1.0);
+	point = rotatePoint(center, vec2(sp0.x + size, sp0.y + size), angle);
+	gl_Position = vec4(point / Viewport, getZdepth(P0), 1.0);
 	EmitVertex();
 
 	mTexCoord = rotateUV(vec2(1, 0), finaluvdata[0].y);
 	mColor = finalColor[0];
-	gl_Position = vec4(vec2(sp0.x + size, sp0.y - size * aspect) / Viewport, getZdepth(P0), 1.0);
+	point = rotatePoint(center, vec2(sp0.x + size, sp0.y - size), angle);
+	gl_Position = vec4(point / Viewport, getZdepth(P0), 1.0);
 	EmitVertex();
 
 	EndPrimitive();