--- a/hedgewars/uCollisions.pas	Sun May 02 16:16:00 2010 +0000
+++ b/hedgewars/uCollisions.pas	Sun May 02 16:24:31 2010 +0000
@@ -49,6 +49,8 @@
 function  TestCollisionXwithXYShift(Gear: PGear; ShiftX: hwFloat; ShiftY: LongInt; Dir: LongInt): boolean;
 function  TestCollisionYwithXYShift(Gear: PGear; ShiftX, ShiftY: LongInt; Dir: LongInt): boolean;
 
+function  calcSlopeNormal(Gear: PGear; collisionX, collisionY: LongInt; var deltaX, deltaY: LongInt; TestWord: LongWord): Boolean;
+
 implementation
 uses uMisc, uConsts, uLand, uLandGraphics, uConsole;
 
@@ -312,6 +314,187 @@
 Gear^.Y:= Gear^.Y - int2hwFloat(ShiftY)
 end;
 
+
+function calcSlopeNormal(Gear: PGear; collisionX, collisionY: LongInt; var deltaX, deltaY: LongInt; TestWord: LongWord): boolean;
+var sx, sy, ldx, ldy, rdx, rdy: LongInt;
+    i, j, mx, my : ShortInt;
+    tmpx, tmpy: LongWord;
+    dx, dy, rx, ry: hwFloat;
+    leftsteps:  Array[0..4,0..1] of ShortInt;
+    rightsteps: Array[0..4,0..1] of ShortInt;
+
+begin
+    dx:= Gear^.dX;
+    dy:= Gear^.dY;
+    
+    if Gear^.AdvBounce > 0 then
+        begin
+        rx:= _0_5 + Int2hwFloat(collisionX) - Gear^.X;
+        ry:= _0_5 + Int2hwFloat(collisionY) - Gear^.Y;
+        end
+    else
+        begin
+        rx:= dx;
+        ry:= dy;
+        end;
+
+    sx:= hwSign(rx);
+    sy:= hwSign(ry);
+
+    if rx.QWordValue > ry.QWordValue then
+        begin
+        if (ry/rx).QWordValue < _0_5.QWordValue then sy:= 0;
+        end
+    else
+        begin
+        if (rx/ry).QWordValue < _0_5.QWordValue then sx:= 0;
+        end;
+
+    mx:= -sx;
+    my:= -sy;
+
+    for i:= 0 to 4 do
+        begin
+        if (mx = -1) and (my <>  1) then my:= my + 1
+        else if (my = 1) and (mx <> 1) then mx:= mx + 1
+        else if (mx = 1) and (my <> -1) then my:= my - 1
+        else mx:= mx - 1;
+
+        leftsteps[i,0]:= mx;
+        leftsteps[i,1]:= my;
+        end;
+
+    mx:= -sx;
+    my:= -sy;
+
+    for i:= 0 to 4 do
+        begin
+        if (mx = -1) and (my <> -1) then my:= my - 1
+        else if (my = -1) and (mx <> 1) then mx:= mx + 1
+        else if (mx = 1) and (my <> 1) then my:= my + 1
+        else mx:= mx - 1;
+
+        rightsteps[i,0]:= mx;
+        rightsteps[i,1]:= my;
+        end;
+
+    ldx:= collisionX;
+    ldy:= collisionY;
+    rdx:= collisionX;
+    rdy:= collisionY;
+
+    for i:= 0 to 4 do
+        begin
+        tmpx:= collisionX + leftsteps[i,0];
+        tmpy:= collisionY + leftsteps[i,1];
+        if (((tmpy) and LAND_HEIGHT_MASK) = 0) and (((tmpx) and LAND_WIDTH_MASK)  = 0) then
+            if (Land[tmpy,tmpx] > TestWord) then
+                begin
+                if i <> 0 then
+                    for j:= 0 to 2 do
+                        begin
+                        leftsteps[j,0]:= leftsteps[i+j,0];
+                        leftsteps[j,1]:= leftsteps[i+j,1];
+                        end;
+                ldx:= tmpx;
+                ldy:= tmpy;
+                break;
+                end;
+        end;
+
+    for i:= 0 to 4 do
+        begin
+        tmpx:= collisionX + rightsteps[i,0];
+        tmpy:= collisionY + rightsteps[i,1];
+        if (((tmpy) and LAND_HEIGHT_MASK) = 0) and (((tmpx) and LAND_WIDTH_MASK)  = 0) then
+            if (Land[tmpy,tmpx] > TestWord) then
+                begin
+                if i <> 0 then
+                    for j:= 0 to 2 do
+                        begin
+                        rightsteps[j,0]:= rightsteps[i+j-1,0];
+                        rightsteps[j,1]:= rightsteps[i+j-1,1];
+                        end;
+                rdx:= tmpx;
+                rdy:= tmpy;
+                break;
+                end;
+        end;
+
+    // TODO: avoid redundant checks
+    for i:= 0 to 4 do
+        begin
+        for j:= 0 to 2 do
+            begin
+            tmpx:= ldx + leftsteps[j,0];
+            tmpy:= ldy + leftsteps[j,1];
+            if (((tmpy) and LAND_HEIGHT_MASK) = 0) and (((tmpx) and LAND_WIDTH_MASK)  = 0) then
+                if (Land[tmpy,tmpx] > TestWord) then
+                    begin
+                    ldx:= tmpx;
+                    ldy:= tmpy;
+                    break;
+                    end;
+            end;
+        end;
+
+    for i:= 0 to 4 do
+        begin
+        for j:= 0 to 2 do
+            begin
+            tmpx:= rdx + rightsteps[j,0];
+            tmpy:= rdy + rightsteps[j,1];
+            if (((tmpy) and LAND_HEIGHT_MASK) = 0) and (((tmpx) and LAND_WIDTH_MASK)  = 0) then
+                if (Land[tmpy,tmpx] > TestWord) then
+                    begin
+                    rdx:= tmpx;
+                    rdy:= tmpy;
+                    break;
+                    end;
+            end;
+        end;
+
+    ldx:= rdx - ldx;
+    ldy:= rdy - ldy;
+
+    // rotate vector by 90°
+    rdx:= -ldy;
+    ldy:= ldx;
+    ldx:= rdx;
+    
+    if (ldy <> 0) then tmpy := collisionY + ldy div abs(ldy) else tmpy:= collisionY;
+    if (ldx <> 0) then tmpx := collisionX + ldx div abs(ldx) else tmpx:= collisionX;
+    if ((ldx = 0) and (ldy = 0)) then EXIT(false);
+    
+    if ((((tmpy) and LAND_HEIGHT_MASK) = 0) and (((tmpx) and LAND_WIDTH_MASK)  = 0) 
+        and (Land[tmpy,tmpx] > TestWord)) then
+            begin
+            if (ldy <> 0) then
+                begin
+                ldy:= -ldy;
+                tmpy := collisionY + ldy div abs(ldy);
+                end;
+            if (ldx <> 0) then
+                begin
+                ldx:= -ldx;
+                tmpx := collisionX + ldx div abs(ldx);
+                end;
+            
+            if ((((tmpy) and LAND_HEIGHT_MASK) = 0) and (((tmpx) and LAND_WIDTH_MASK)  = 0) 
+                and (Land[tmpy,tmpx] > TestWord)) then
+                    EXIT(false);
+            end;
+
+        
+    if (dx*ldx + dy*ldy).isNegative then
+        begin
+        deltaX:= ldx;
+        deltaY:= ldy;
+        EXIT(true);
+        end;
+exit(false);
+end;
+
 procedure initModule;
 begin
     Count:= 0;