nicoptere · July 19, 2017 12:52 · Jul 19, 2017
diff --git a/affine transform b/affine transform
@@ -0,0 +1,100 @@
+//from https://math.stackexchange.com/questions/296794/finding-the-transform-matrix-from-4-projected-points-with-javascript/339033#339033
+// and http://jsfiddle.net/dFrHS/1/
+
+function adj(m) { // Compute the adjugate of m
+    return [
+        m[4]*m[8]-m[5]*m[7], m[2]*m[7]-m[1]*m[8], m[1]*m[5]-m[2]*m[4],
+        m[5]*m[6]-m[3]*m[8], m[0]*m[8]-m[2]*m[6], m[2]*m[3]-m[0]*m[5],
+        m[3]*m[7]-m[4]*m[6], m[1]*m[6]-m[0]*m[7], m[0]*m[4]-m[1]*m[3]
+    ];
+}
+function multmm(a, b) { // multiply two matrices
+    var c = new Float32Array(9);
+    for (var i = 0; i != 3; ++i) {
+        for (var j = 0; j != 3; ++j) {
+            var cij = 0;
+            for (var k = 0; k != 3; ++k) {
+                cij += a[3*i + k]*b[3*k + j];
+            }
+            c[3*i + j] = cij;
+        }
+    }
+    return c;
+}
+function general2DProjection(x1s, y1s, x2s, y2s, x3s, y3s, x1d, y1d, x2d, y2d, x3d, y3d) {
+    var s = [
+        x1s, x2s, x3s,
+        y1s, y2s, y3s,
+        1, 1, 1
+    ];
+    var d = [
+        x1d, x2d, x3d,
+        y1d, y2d, y3d,
+        1, 1, 1
+    ];
+    return multmm(d, adj(s));
+}
+function transform2d( x1, y1, x2, y2, x3, y3) {
+    var w = 100;
+    var h = 100;
+    var t = general2DProjection(0, 0, w, 0, 0, h, x1, y1, x2, y2, x3, y3 );
+    for(i = 0; i != 9; ++i) t[i] = t[i]/t[8];
+    return [t[0], t[3], 0, t[6], t[1], t[4], 0, t[7], 0   , 0   , 1, 0   , t[2], t[5], 0, t[8] ];
+}
+
+
+/*
+//compacted
+    function transform2d( src, dest ) {
+        var t =  multmm(
+                [ dest[0], dest[2], dest[4], dest[1], dest[3], dest[5], 1,1,1 ],
+                adj( [ src[0], src[2], src[4], src[1], src[3], src[5], 1,1,1 ] )
+        );
+        return [t[0], t[3], 0, t[6], t[1], t[4], 0, t[7], 0   , 0   , 1, 0   , t[2], t[5], 0, t[8] ];
+    }
+//*/
+
+
+for THREE
+
+function adjugate(m) {
+    return [
+        m[4] * m[8] - m[5] * m[7], m[2] * m[7] - m[1] * m[8], m[1] * m[5] - m[2] * m[4],
+        m[5] * m[6] - m[3] * m[8], m[0] * m[8] - m[2] * m[6], m[2] * m[3] - m[0] * m[5],
+        m[3] * m[7] - m[4] * m[6], m[1] * m[6] - m[0] * m[7], m[0] * m[4] - m[1] * m[3]
+    ];
+}
+
+function multiplyMatrices(a, b) {
+    var c = new Float32Array(9);
+    for (var i = 0; i != 3; ++i) {
+        for (var j = 0; j != 3; ++j) {
+            var cij = 0;
+            for (var k = 0; k != 3; ++k) {
+                cij += a[3 * i + k] * b[3 * k + j];
+            }
+            c[3 * i + j] = cij;
+        }
+    }
+    return c;
+}
+
+function affineTransform(src, dst) {
+    var t = multiplyMatrices(
+            [dst[0], dst[2], dst[4], dst[1], dst[3], dst[5], 1, 1, 1],
+            adjugate([src[0], src[2], src[4], src[1], src[3], src[5], 1, 1, 1])
+    );
+    return [t[0], t[3], 0, t[6], t[1], t[4], 0, t[7], 0, 0, 1, 0, t[2], t[5], 0, t[8]];
+}
+
+
+function getTrMatrix( s0, s1, s2, d0, d1, d2 ) {
+
+    var src = [ s0.x, s0.y, s1.x, s1.y, s2.x, s2.y];
+    var dst = [ d0.x, d0.y, d1.x, d1.y, d2.x, d2.y];
+    var t = affineTransform( src, dst );
+    var mat = new THREE.Matrix4();
+    mat.elements = t;
+    return mat;
+
+}