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SCI: Add GetAngle for SCI1 that matches SSCI

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Thanks to waltervn for creating a scis test script to verify.
This commit is contained in:
Willem Jan Palenstijn 2013-01-24 22:08:06 +01:00
parent b0cfe968b0
commit 89cd5e7416
1 changed files with 70 additions and 12 deletions
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82
engines/sci/engine/kmath.cpp
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@ -77,18 +77,7 @@ reg_t kSqrt(EngineState *s, int argc, reg_t *argv) {
return make_reg(0, (int16) sqrt((float) ABS(argv[0].toSint16())));
}
/**
* Returns the angle (in degrees) between the two points determined by (x1, y1)
* and (x2, y2). The angle ranges from 0 to 359 degrees.
* What this function does is pretty simple but apparently the original is not
* accurate.
*/
uint16 kGetAngleWorker(int16 x1, int16 y1, int16 x2, int16 y2) {
// SCI1 games (QFG2 and newer) use a simple atan implementation. SCI0 games
// use a somewhat less accurate calculation (below).
if (getSciVersion() >= SCI_VERSION_1_EGA_ONLY)
return (int16)(360 - atan2((double)(x1 - x2), (double)(y1 - y2)) * 180 / M_PI + 0.5) % 360;
uint16 kGetAngle_SCI0(int16 x1, int16 y1, int16 x2, int16 y2) {
int16 xRel = x2 - x1;
int16 yRel = y1 - y2; // y-axis is mirrored.
int16 angle;
@ -118,6 +107,75 @@ uint16 kGetAngleWorker(int16 x1, int16 y1, int16 x2, int16 y2) {
return angle;
}
// atan2 for first octant, x >= y >= 0. Returns [0,45] (inclusive)
int kGetAngle_SCI1_atan2_base(int y, int x) {
if (x == 0)
return 0;
// fixed point tan(a)
int tan_fp = 10000 * y / x;
if ( tan_fp >= 1000 ) {
// For tan(a) >= 0.1, interpolate between multiples of 5 degrees
// 10000 * tan([5, 10, 15, 20, 25, 30, 35, 40, 45])
const int tan_table[] = { 875, 1763, 2679, 3640, 4663, 5774,
7002, 8391, 10000 };
// Look up tan(a) in our table
int i = 1;
while (tan_fp > tan_table[i]) ++i;
// The angle a is between 5*i and 5*(i+1). We linearly interpolate.
int dist = tan_table[i] - tan_table[i-1];
int interp = (5 * (tan_fp - tan_table[i-1]) + dist/2) / dist;
return 5*i + interp;
} else {
// for tan(a) < 0.1, tan(a) is approximately linear in a.
// tan'(0) = 1, so in degrees the slope of atan is 180/pi = 57.29...
return (57 * y + x/2) / x;
}
}
int kGetAngle_SCI1_atan2(int y, int x) {
if (y < 0) {
int a = kGetAngle_SCI1_atan2(-y, -x);
if (a == 180)
return 0;
else
return 180 + a;
}
if (x < 0)
return 90 + kGetAngle_SCI1_atan2(-x, y);
if (y > x)
return 90 - kGetAngle_SCI1_atan2_base(x, y);
else
return kGetAngle_SCI1_atan2_base(y, x);
}
uint16 kGetAngle_SCI1(int16 x1, int16 y1, int16 x2, int16 y2) {
// We flip things around to get into the standard atan2 coordinate system
return kGetAngle_SCI1_atan2(x2 - x1, y1 - y2);
}
/**
* Returns the angle (in degrees) between the two points determined by (x1, y1)
* and (x2, y2). The angle ranges from 0 to 359 degrees.
* What this function does is pretty simple but apparently the original is not
* accurate.
*/
uint16 kGetAngleWorker(int16 x1, int16 y1, int16 x2, int16 y2) {
if (getSciVersion() >= SCI_VERSION_1_EGA_ONLY)
return kGetAngle_SCI1(x1, y1, x2, y2);
else
return kGetAngle_SCI0(x1, y1, x2, y2);
}
reg_t kGetAngle(EngineState *s, int argc, reg_t *argv) {
// Based on behavior observed with a test program created with
// SCI Studio.