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authorEric Anholt <[email protected]>2008-02-06 15:38:16 -0800
committerEric Anholt <[email protected]>2008-02-06 15:40:32 -0800
commit2551a5ee80ab523006618c79766e2409b2a62d84 (patch)
treeccdd6c390e27abe28a7fb6583d5098aa41db0ae5 /src/mesa
parentd98abcbef0bd4200fc0fd30fc0524bf452df3572 (diff)
[915] Use a quartic term to improve the accuracy of SIN results.
This is described in the link in the comment, and is the same technique that r300 uses.
Diffstat (limited to 'src/mesa')
-rw-r--r--src/mesa/drivers/dri/i915/i915_fragprog.c77
1 files changed, 54 insertions, 23 deletions
diff --git a/src/mesa/drivers/dri/i915/i915_fragprog.c b/src/mesa/drivers/dri/i915/i915_fragprog.c
index 0a643719f88..cbac07cde16 100644
--- a/src/mesa/drivers/dri/i915/i915_fragprog.c
+++ b/src/mesa/drivers/dri/i915/i915_fragprog.c
@@ -43,11 +43,19 @@
#include "i915_context.h"
#include "i915_program.h"
-static const GLfloat sin_quad_constants[4] = {
- 4.0,
- -4.0,
- 2.0,
- -1.0
+static const GLfloat sin_quad_constants[2][4] = {
+ {
+ 2.0,
+ -1.0,
+ .5,
+ 0.0
+ },
+ {
+ 4.0,
+ -4.0,
+ 1.0 / (2.0 * M_PI),
+ .2225
+ }
};
static const GLfloat sin_constants[4] = { 1.0,
@@ -341,7 +349,7 @@ upload_program(struct i915_fragment_program *p)
while (1) {
GLuint src0, src1, src2, flags;
- GLuint tmp = 0, consts = 0;
+ GLuint tmp = 0, consts0 = 0, consts1 = 0;
switch (inst->Opcode) {
case OPCODE_ABS:
@@ -690,15 +698,16 @@ upload_program(struct i915_fragment_program *p)
case OPCODE_SIN:
src0 = src_vector(p, &inst->SrcReg[0], program);
tmp = i915_get_utemp(p);
- consts = i915_emit_const4fv(p, sin_quad_constants);
+ consts0 = i915_emit_const4fv(p, sin_quad_constants[0]);
+ consts1 = i915_emit_const4fv(p, sin_quad_constants[1]);
/* Reduce range from repeating about [-pi,pi] to [-1,1] */
i915_emit_arith(p,
A0_MAD,
tmp, A0_DEST_CHANNEL_X, 0,
src0,
- i915_emit_const1f(p, 1.0 / (2.0 * M_PI)),
- i915_emit_const1f(p, .5));
+ swizzle(consts1, Z, ZERO, ZERO, ZERO), /* 1/(2pi) */
+ swizzle(consts0, Z, ZERO, ZERO, ZERO)); /* .5 */
i915_emit_arith(p, A0_FRC, tmp, A0_DEST_CHANNEL_X, 0, tmp, 0, 0);
@@ -706,19 +715,15 @@ upload_program(struct i915_fragment_program *p)
A0_MAD,
tmp, A0_DEST_CHANNEL_X, 0,
tmp,
- swizzle(consts, Z, ZERO, ZERO, ZERO), /* 2 */
- swizzle(consts, W, ZERO, ZERO, ZERO)); /* -1 */
+ swizzle(consts0, X, ZERO, ZERO, ZERO), /* 2 */
+ swizzle(consts0, Y, ZERO, ZERO, ZERO)); /* -1 */
- /* Compute sin using a quadratic. While it has increased total
- * error over the range, it does give continuity that the 4-component
- * Taylor series lacks when repeating the range due to its
- * sin(PI) != 0 behavior.
+ /* Compute sin using a quadratic and quartic. It gives continuity
+ * that repeating the Taylor series lacks every 2*pi, and has
+ * reduced error.
*
* The idea was described at:
* http://www.devmaster.net/forums/showthread.php?t=5784
- *
- * If we're concerned about the error of this approximation, we should
- * probably incorporate a second pass to include a x**4 factor.
*/
/* tmp.y = abs(tmp.x); {x, abs(x), 0, 0} */
@@ -737,15 +742,41 @@ upload_program(struct i915_fragment_program *p)
tmp,
0);
- /* result = tmp.xy DP sin_quad_constants.xy */
+ /* tmp.x = tmp.xy DP sin_quad_constants[2].xy */
i915_emit_arith(p,
A0_DP3,
+ tmp, A0_DEST_CHANNEL_X, 0,
+ tmp,
+ swizzle(consts1, X, Y, ZERO, ZERO),
+ 0);
+
+ /* tmp.x now contains a first approximation (y). Now, weight it
+ * against tmp.y**2 to get closer.
+ */
+ i915_emit_arith(p,
+ A0_MAX,
+ tmp, A0_DEST_CHANNEL_Y, 0,
+ swizzle(tmp, ZERO, X, ZERO, ZERO),
+ negate(swizzle(tmp, ZERO, X, ZERO, ZERO), 0, 1, 0, 0),
+ 0);
+
+ /* tmp.y = tmp.x * tmp.y - tmp.x; {y, y * abs(y) - y, 0, 0} */
+ i915_emit_arith(p,
+ A0_MAD,
+ tmp, A0_DEST_CHANNEL_Y, 0,
+ swizzle(tmp, ZERO, X, ZERO, ZERO),
+ swizzle(tmp, ZERO, Y, ZERO, ZERO),
+ negate(swizzle(tmp, ZERO, X, ZERO, ZERO), 0, 1, 0, 0));
+
+ /* result = .2225 * tmp.y + tmp.x =.2225(y * abs(y) - y) + y= */
+ i915_emit_arith(p,
+ A0_MAD,
get_result_vector(p, inst),
get_result_flags(inst), 0,
- tmp,
- swizzle(i915_emit_const4fv(p, sin_quad_constants),
- X, Y, ZERO, ZERO),
- 0);
+ swizzle(consts1, W, W, W, W),
+ swizzle(tmp, Y, Y, Y, Y),
+ swizzle(tmp, X, X, X, X));
+
break;
case OPCODE_SLT: