flug:

* fix the 'slanting shadow > 75 meters' problem
* lay down the shadow flat on the ground

wlbragg:
* add fading effect based o altitude

Shaders/shadow-ALS.frag

@@ -2,6 +2,7 @@
 
 uniform sampler2D texture;
 uniform float scattering;
+varying float alpha_correction;
 
 void main()
 {
@@ -15,5 +16,5 @@ void main()
     texel.a = min(0.8, texel.a);
 
     vec4 fragColor = texel;
-    gl_FragColor = fragColor;
+    gl_FragColor = fragColor * alpha_correction;;
 }

Shaders/shadow-vol-ALS.vert

@@ -23,11 +23,23 @@ const float terminator_width = 200000.0;
 void rotationMatrixPR(in float sinRx, in float cosRx, in float sinRy, in float cosRy, out mat4 rotmat)
 {
    rotmat = mat4(   cosRy ,   sinRx * sinRy ,   cosRx * sinRy,   0.0,
-									0.0   ,	cosRx        ,	-sinRx * cosRx,	0.0,
+                           0.0   ,   cosRx        ,   -sinRx      ,   0.0,
                            -sinRy,   sinRx * cosRy,   cosRx * cosRy ,   0.0,
                            0.0   ,   0.0          ,   0.0           ,   1.0 );
 }
 
+/*
+
+//Experimental - not used for now.  Seems to work functionally the same as rotationMatrixPR
+void rotationMatrixRP(in float sinRx, in float cosRx, in float sinRy, in float cosRy, out mat4 rotmat)
+{
+   rotmat = mat4(   cosRy ,   sinRx * sinRy ,   -cosRx * sinRy,   0.0,
+                           0.0   ,   cosRx        ,   sinRx      ,   0.0,
+                           sinRy,   -sinRx * cosRy,   cosRx * cosRy ,   0.0,
+                           0.0   ,   0.0          ,   0.0           ,   1.0 );
+}
+*/
+
 float light_func (in float x, in float a, in float b, in float c, in float d, in float e)
 {
 
@@ -36,9 +48,14 @@ if (x < -15.0) {return 0.0;}
 return e / pow((1.0 + a * exp(-b * (x-c)) ),(1.0/d));
 }
 
+varying float alpha_correction;
+
 void main()
 {
-
+    float start_fade = 0;
+    float end_fade = 100;
+    float diff = end_fade - start_fade;
+    alpha_correction = 1.0 - smoothstep(start_fade, end_fade, alt_agl);
 
     gl_TexCoord[0] = gl_TextureMatrix[0] * gl_MultiTexCoord0;
 
@@ -65,36 +82,80 @@ void main()
 
     light_diffuse.rgb = light_diffuse.rgb * (1.0 + 1.2 * shade_depth);
 
+    //experiment
+    light_diffuse.b = 1.0;
+    light_diffuse.g = 1.0;
+    light_diffuse.r = 1.0;
+    light_diffuse.a = 1.0;
 
    //prepare rotation matrix
    mat4 RotMatPR;
+   mat4 RotMatPR_tr;
 
    float _roll = roll;
 
 
-   if (_roll>90.0 || _roll < -90.0)
-	{_roll = -_roll;}
-   float cosRx = cos(radians(_roll));
-   float sinRx = sin(radians(_roll));
-   float cosRy = cos(radians(-pitch));
-   float sinRy = sin(radians(-pitch));
+   //if (_roll>90.0 || _roll < -90.0) //making roll=-roll when >90 is no longer necessary thanks to fix with transpose of rotation matrix.
+    //{_roll = -_roll;}
+   float cosRx = cos(radians(-_roll));
+   float sinRx = sin(radians(-_roll));
+   float cosRy = cos(radians(pitch));
+   float sinRy = sin(radians(pitch));
 
    rotationMatrixPR(sinRx, cosRx, sinRy, cosRy, RotMatPR);
+   //rotationMatrixRP(sinRx, cosRx, sinRy, cosRy, RotMatPR);
+
+   RotMatPR_tr=transpose(RotMatPR); //RotMatPR works fine if pitch =0 or roll=0 but if say pitch=35 and roll=60 the rotation is all wrong. transpose(RotMatPR) however works perfectly.
 
 
     // project the shadow onto the ground
-    vec4 vertex =   RotMatPR * gl_Vertex;
+    //vec4 vertex =   RotMatPR * gl_Vertex;
+    vec4 vertex =   RotMatPR_tr * gl_Vertex;
     vec4 pos = vertex;
+
+    vec2 deltaxy = lightFull.xy * 0.95* (alt_agl + vertex.z + gear_clearance)/lightFull.z;  //This is the 'actual' location, taking into a account the full 3-D structure of the aircraft
+
+    vec2 deltazeroxy = lightFull.xy * 0.95* (alt_agl + gear_clearance)/lightFull.z; //Instead of using the exact z value of this particularly point to determine the distance of the shadow & reposition & shrink it appropriately, we'll just use the origin (0,0,0) of the model instead.  This avoids a problem below, where varying vertex.z in deltaxy and then using deltaxy to calculate dist caused the shadow to sort of slant upwards, thanks to the varying z values used
+
+    float dist = sqrt(deltazeroxy.x * deltazeroxy.x + deltazeroxy.y * deltazeroxy.y + alt_agl * alt_agl);    //could use function 'distance' instead, might be better?
+
+
+    if (dist < 75)
+    {
+
          pos.z = -0.9 * alt_agl + 0.05 * vertex.z;
          //pos.z  = 0.05 * (vertex.z + gear_clearance);
 
+         pos.xy -= deltaxy;
+
+    }
+    else
+    {
+         //The code below to shrink the shadow while keeping it 75 m. away has some issues that need to be fixed. Making the shadow shrink at x^2 rate partly to cover up this problem until it can be solved . . .
+         //The problem is that the aircraft isn't flat/parallel to the ground any more, but it appears to be at an angle to the ground.
+         //The various shrinkages perhaps mess with the angles somehow, meaning that when the animations apply the roll & pitch corrections they just don't quite work as they should
+         pos.z = (-0.9*75)*alt_agl/dist + 0.05 * vertex.z ; //if the shadow is more than about 75 meters from the aircraft it disappears so we are going to just keep it right at 75 m. & make it smaller to simulate greater distance.
+         //(-0.9*75) is the same factor for altitude we were using above when dist=75.  *alt_agl/dist keeps it at the right height proportionally to simulate the location at a further distance, while actually just keeping it at 75 m. distance.
+
+         //pos.z = 0.05 * vertex.z ; //if the shadow is more than about 75 meters from the aircraft it disappears so we are going to just keep it right at 75 m. & make it smaller to simulate greater distance.
+
+
+
+         //shrink the size FIRST, THEN move where it needs to be.  If you shrink later you're also shrinking the deltaxy distance moved, which doesn't work well
+         pos.xy = 75 / dist * pos.xy;  //shrinking the size of the shadow to simulate further distance.  Should be linear shrinkage but doing it ^2 for now to help ucover up the issues in code above.
+
+         pos.xy -= 75 * deltaxy/dist; // Similarly to above, * deltaxy/dist; keeps it at the right XY position proportionally to simulate the location at a further distance, while actually just keeping it at 75 m. distance.
+
+    }
+
    // pos.z = pos.z - offset;
-    pos.xy -= lightFull.xy * 0.95* (alt_agl + vertex.z + gear_clearance)/lightFull.z;
-
 
+   //if (dist>=75) pos = pos * 30/dist; //not sure why this doesn't work/ perhaps an overflow of some kind?
    
     gl_Position =  gl_ModelViewProjectionMatrix * pos;
 
     gl_FrontColor = light_diffuse;
+    //light_diffuse.a=0;
     gl_BackColor = gl_FrontColor;
+    //gl_BackColor = light_diffuse;
 }