ccdGJKPenetration does not calculate exact contact location on a large box.

[taesoobear]

I am trying to use libccd for my QP-based physics simulator, because libccd is very clean and compact. Thank you very much for such a nice library.
(Previously, I used btGjkEpaSolver in bullet-2.68.)
In my tests, everything seemed to work perfectly, unless a box (or any other convex objects) is large.
When a box is large, box-box collision test works fine, but ccdGJKPeneration provides incorrect contact location. The contact normal and depth are accurate, and only the location is off.
This is so only when a box is much larger than the other box. For example, when one box is 5 meters big while the other box is 0.2 meter big, the results are always inconsistent and inaccurate.
I wonder if this is a known problem, or am I doing something wrong?
I wrote my code based on testsuites/boxbox.c, and used the ccdSupport function in testsuites/support.c.
I am using a Ubuntu machine. libccd was pulled from here a few days ago. (HASH:842646...)
But my code has other dependencies so I did not post here.

[UPDATE]
This issue has gone when I switched to ccdMPRPenetration. MPRPenetration seems to be less accurate about idepth though.

[danfis]

Could you create unit tests and send them to me (the best way would be a pull request). Then we can try to find out where is the problem and fix it.

[taesoobear]

Shown below is the unit tests that fail only for ccdGJKpenetration. Thanks much.

From 65a053ff38fdb8172d30356a04e8f9611fbdea54 Mon Sep 17 00:00:00 2001
From: taesoo kwon [email protected]
Date: Tue, 15 Mar 2016 22:03:37 +0900
Subject: [PATCH 1/1] a

---

src/testsuites/boxbox.c | 31 +++++++++++++++++++++++++++++++
src/testsuites/boxbox.h | 2 ++
src/testsuites/mpr_boxbox.c | 33 +++++++++++++++++++++++++++++++++
src/testsuites/mpr_boxbox.h | 2 ++
4 files changed, 68 insertions(+)

diff --git a/src/testsuites/boxbox.c b/src/testsuites/boxbox.c
index 314d134..d76b373 100644
--- a/src/testsuites/boxbox.c
+++ b/src/testsuites/boxbox.c
@@ -464,3 +464,34 @@ TEST(boxboxPenetration)
recPen(depth, &dir, &pos, stdout, "Pen 8");
//TOSVT();
}
+TEST(boxboxPenetration2)
+{

• ccd_t ccd;
• CCD_BOX(box1);
• CCD_BOX(box2);
• int res;
• ccd_real_t depth;
• ccd_vec3_t dir, pos;

• fprintf(stderr, "\n\n\n---- boxboxPenetration ----\n\n\n");

• box1.x = 20;
• box1.y = 0.1;
• box1.z = 20;
• box2.x = 0.2;
• box2.y = 0.15;
• box2.z = 0.2;

• CCD_INIT(&ccd);
• ccd.support1 = ccdSupport;
• ccd.support2 = ccdSupport;

• ccdVec3Set(&box2.pos, 0, 0.1, 0.);
• res = ccdGJKPenetration(&box1, &box2, &ccd, &depth, &dir, &pos);
• assertTrue(res == 0);
• recPen(depth, &dir, &pos, stdout, "Pen largeBox");
• assertTrue(-0.2 < pos.v[0] && pos.v[0] <0.2);
• //TOSVT();

+}
diff --git a/src/testsuites/boxbox.h b/src/testsuites/boxbox.h
index 8127c7c..4d88464 100644
--- a/src/testsuites/boxbox.h
+++ b/src/testsuites/boxbox.h
@@ -14,6 +14,7 @@ TEST(boxboxRot);

TEST(boxboxSeparate);
TEST(boxboxPenetration);
+TEST(boxboxPenetration2);

TEST_SUITE(TSBoxBox) {
TEST_ADD(boxboxSetUp),
@@ -24,6 +25,7 @@ TEST_SUITE(TSBoxBox) {
TEST_ADD(boxboxRot),
TEST_ADD(boxboxSeparate),
TEST_ADD(boxboxPenetration),

• TEST_ADD(boxboxPenetration2),

TEST_ADD(boxboxTearDown),
TEST_SUITE_CLOSURE
diff --git a/src/testsuites/mpr_boxbox.c b/src/testsuites/mpr_boxbox.c
index 22f0a31..4771495 100644
--- a/src/testsuites/mpr_boxbox.c
+++ b/src/testsuites/mpr_boxbox.c
@@ -500,3 +500,36 @@ TEST(mprBoxboxPenetration)
recPen(depth, &dir, &pos, stdout, "Pen 10");
//TOSVT();
}
+TEST(mprBoxboxPenetration2)
+{

• ccd_t ccd;
• CCD_BOX(box1);
• CCD_BOX(box2);
• int res;
• ccd_real_t depth;
• ccd_vec3_t dir, pos;

• fprintf(stderr, "\n\n\n---- boxboxPenetration ----\n\n\n");

• box1.x = 20;
• box1.y = 0.1;
• box1.z = 20;
• box2.x = 0.2;
• box2.y = 0.15;
• box2.z = 0.2;

• CCD_INIT(&ccd);
• ccd.support1 = ccdSupport;
• ccd.support2 = ccdSupport;
• ccd.center1 = ccdObjCenter;
• ccd.center2 = ccdObjCenter;

• ccdVec3Set(&box2.pos, 0, 0.1, 0.);
• res = ccdMPRPenetration(&box1, &box2, &ccd, &depth, &dir, &pos);
• assertTrue(res == 0);
• recPen(depth, &dir, &pos, stdout, "Pen largeBox mpr");
• assertTrue(-0.2 < pos.v[0] && pos.v[0] <0.2);
• //TOSVT();

+}
diff --git a/src/testsuites/mpr_boxbox.h b/src/testsuites/mpr_boxbox.h
index 2f29ad7..283fb6f 100644
--- a/src/testsuites/mpr_boxbox.h
+++ b/src/testsuites/mpr_boxbox.h
@@ -11,6 +11,7 @@ TEST(mprBoxboxRot);

TEST(mprBoxboxSeparate);
TEST(mprBoxboxPenetration);
+TEST(mprBoxboxPenetration2);

TEST_SUITE(TSMPRBoxBox) {
TEST_ADD(mprBoxboxAlignedX),
@@ -19,6 +20,7 @@ TEST_SUITE(TSMPRBoxBox) {
TEST_ADD(mprBoxboxRot),
TEST_ADD(mprBoxboxSeparate),
TEST_ADD(mprBoxboxPenetration),

• TEST_ADD(mprBoxboxPenetration2),

TEST_SUITE_CLOSURE

};

1.9.1