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Generate a .gif showing a spinning 3d wireframe cube with hidden lines in Golang
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| package main | |
| import ( | |
| "fmt" | |
| "image" | |
| "image/color" | |
| "image/gif" | |
| "math" | |
| "os" | |
| ) | |
| func subVec3(a []float64, b []float64) []float64 { | |
| return []float64{a[0] - b[0], a[1] - b[1], a[2] - b[2], 0} | |
| } | |
| func dotProduct3(a []float64, b []float64) float64 { | |
| return a[0]*b[0] + a[1]*b[1] + a[2]*b[2] | |
| } | |
| func crossProduct3(a []float64, b []float64) []float64 { | |
| return []float64{ | |
| a[1]*b[2] - a[2]*b[1], | |
| a[2]*b[0] - a[0]*b[2], | |
| a[0]*b[1] - a[1]*b[0], | |
| 0} | |
| } | |
| func matMatMult(m4_1 []float64, m4_2 []float64) []float64 { | |
| result := make([]float64, 16) | |
| result[0] += m4_1[0] * m4_2[0] // row 1 x column 1 | |
| result[0] += m4_1[1] * m4_2[4] | |
| result[0] += m4_1[2] * m4_2[8] | |
| result[0] += m4_1[3] * m4_2[12] | |
| result[1] += m4_1[0] * m4_2[1] // row 1 x column 2 | |
| result[1] += m4_1[1] * m4_2[5] | |
| result[1] += m4_1[2] * m4_2[9] | |
| result[1] += m4_1[3] * m4_2[13] | |
| result[2] += m4_1[0] * m4_2[2] | |
| result[2] += m4_1[1] * m4_2[6] | |
| result[2] += m4_1[2] * m4_2[10] | |
| result[2] += m4_1[3] * m4_2[14] | |
| result[3] += m4_1[0] * m4_2[3] | |
| result[3] += m4_1[1] * m4_2[7] | |
| result[3] += m4_1[2] * m4_2[11] | |
| result[3] += m4_1[3] * m4_2[15] | |
| result[4] += m4_1[4] * m4_2[0] | |
| result[4] += m4_1[5] * m4_2[4] | |
| result[4] += m4_1[6] * m4_2[8] | |
| result[4] += m4_1[7] * m4_2[12] | |
| result[5] += m4_1[4] * m4_2[1] | |
| result[5] += m4_1[5] * m4_2[5] | |
| result[5] += m4_1[6] * m4_2[9] | |
| result[5] += m4_1[7] * m4_2[13] | |
| result[6] += m4_1[4] * m4_2[2] | |
| result[6] += m4_1[5] * m4_2[6] | |
| result[6] += m4_1[6] * m4_2[10] | |
| result[6] += m4_1[7] * m4_2[14] | |
| result[7] += m4_1[4] * m4_2[3] | |
| result[7] += m4_1[5] * m4_2[7] | |
| result[7] += m4_1[6] * m4_2[11] | |
| result[7] += m4_1[7] * m4_2[15] | |
| result[8] += m4_1[8] * m4_2[0] | |
| result[8] += m4_1[9] * m4_2[4] | |
| result[8] += m4_1[10] * m4_2[8] | |
| result[8] += m4_1[11] * m4_2[12] | |
| result[9] += m4_1[8] * m4_2[1] | |
| result[9] += m4_1[9] * m4_2[5] | |
| result[9] += m4_1[10] * m4_2[9] | |
| result[9] += m4_1[11] * m4_2[13] | |
| result[10] += m4_1[8] * m4_2[2] | |
| result[10] += m4_1[9] * m4_2[6] | |
| result[10] += m4_1[10] * m4_2[10] | |
| result[10] += m4_1[11] * m4_2[14] | |
| result[11] += m4_1[8] * m4_2[3] | |
| result[11] += m4_1[9] * m4_2[7] | |
| result[11] += m4_1[10] * m4_2[11] | |
| result[11] += m4_1[11] * m4_2[15] | |
| result[12] += m4_1[12] * m4_2[0] | |
| result[12] += m4_1[13] * m4_2[4] | |
| result[12] += m4_1[14] * m4_2[8] | |
| result[12] += m4_1[15] * m4_2[12] | |
| result[13] += m4_1[12] * m4_2[1] | |
| result[13] += m4_1[13] * m4_2[5] | |
| result[13] += m4_1[14] * m4_2[9] | |
| result[13] += m4_1[15] * m4_2[13] | |
| result[14] += m4_1[12] * m4_2[2] | |
| result[14] += m4_1[13] * m4_2[6] | |
| result[14] += m4_1[14] * m4_2[10] | |
| result[14] += m4_1[15] * m4_2[14] | |
| result[15] += m4_1[12] * m4_2[3] | |
| result[15] += m4_1[13] * m4_2[7] | |
| result[15] += m4_1[14] * m4_2[11] | |
| result[15] += m4_1[15] * m4_2[15] | |
| return result | |
| } | |
| func vecMatMult(v []float64, m []float64) []float64 { | |
| return []float64{ | |
| m[0]*v[0] + m[1]*v[1] + m[2]*v[2] + m[3]*v[3], | |
| m[4]*v[0] + m[5]*v[1] + m[6]*v[2] + m[7]*v[3], | |
| m[8]*v[0] + m[9]*v[1] + m[10]*v[2] + m[11]*v[3], | |
| m[12]*v[0] + m[13]*v[1] + m[14]*v[2] + m[15]*v[3], | |
| } | |
| } | |
| func getTranslMat4(dx float64, dy float64, dz float64) []float64 { | |
| return []float64{ | |
| 1.0, 0.0, 0.0, dx, | |
| 0.0, 1.0, 0.0, dy, | |
| 0.0, 0.0, 1.0, dz, | |
| 0.0, 0.0, 0.0, 1.0, | |
| } | |
| } | |
| func getRotXMat4(phi float64) []float64 { | |
| cos_phi := math.Cos(phi) | |
| sin_phi := math.Sin(phi) | |
| return []float64{ | |
| 1.0, 0.0, 0.0, 0.0, | |
| 0.0, cos_phi, -sin_phi, 0.0, | |
| 0.0, sin_phi, cos_phi, 0.0, | |
| 0.0, 0.0, 0.0, 1.0, | |
| } | |
| } | |
| func getRotYMat4(phi float64) []float64 { | |
| cos_phi := math.Cos(phi) | |
| sin_phi := math.Sin(phi) | |
| return []float64{ | |
| cos_phi, 0.0, sin_phi, 0.0, | |
| 0.0, 1.0, 0.0, 0.0, | |
| -sin_phi, 0.0, cos_phi, 0.0, | |
| 0.0, 0.0, 0.0, 1.0, | |
| } | |
| } | |
| func getRotZMat4(phi float64) []float64 { | |
| cos_phi := math.Cos(phi) | |
| sin_phi := math.Sin(phi) | |
| return []float64{ | |
| cos_phi, -sin_phi, 0.0, 0.0, | |
| sin_phi, cos_phi, 0.0, 0.0, | |
| 0.0, 0.0, 1.0, 0.0, | |
| 0.0, 0.0, 0.0, 1.0, | |
| } | |
| } | |
| func projectVerts(m []float64, srcV [][]float64) [][]float64 { | |
| var result [][]float64 | |
| for _, v3 := range srcV { | |
| v4 := []float64{v3[0], v3[1], v3[2], 1} | |
| pvec := vecMatMult(v4, m) | |
| result = append(result, pvec) | |
| } | |
| return result | |
| } | |
| func perspDiv(srcV4 [][]float64) [][]float64 { | |
| var result [][]float64 | |
| for _, vec4 := range srcV4 { | |
| result = append(result, []float64{vec4[0] / vec4[2], vec4[1] / vec4[2]}) | |
| } | |
| return result | |
| } | |
| func cullBackfaces(viewPoint []float64, srcIdcs [][]uint, worldVerts [][]float64) []int { | |
| var idcs []int | |
| for i, tri := range srcIdcs { | |
| v0 := worldVerts[tri[0]] | |
| v1 := worldVerts[tri[1]] | |
| v2 := worldVerts[tri[2]] | |
| viewPointToTriVec := subVec3(v0, viewPoint) | |
| s10 := subVec3(v1, v0) | |
| s20 := subVec3(v2, v0) | |
| normal := crossProduct3(s10, s20) | |
| dp := dotProduct3(viewPointToTriVec, normal) | |
| if dp > 0 { | |
| idcs = append(idcs, i) | |
| } | |
| } | |
| return idcs | |
| } | |
| func abs(i int) int { | |
| if i < 0 { | |
| return -i | |
| } | |
| return i | |
| } | |
| // Bresenham implementation from https://github.com/eaburns/quart/blob/master/geom/2d_draw.go#L164 | |
| func drawEdge(img *image.Paletted, w, h int, c color.Color, p0, p1 []float64) { | |
| o_x := w / 2 | |
| o_y := h / 2 | |
| ar := float64(w) / float64(h) | |
| x0 := o_x + int(p0[0]*float64(o_x)) | |
| y0 := o_y - int(p0[1]*float64(o_y)*ar) | |
| x1 := o_x + int(p1[0]*float64(o_x)) | |
| y1 := o_y - int(p1[1]*float64(o_y)*ar) | |
| // Bresenham's alg: http://en.wikipedia.org/wiki/Bresenham's_line_algorithm | |
| steep := abs(y0-y1) > abs(x0-x1) | |
| if steep { | |
| x0, y0 = y0, x0 | |
| x1, y1 = y1, x1 | |
| } | |
| if x0 > x1 { | |
| x0, x1 = x1, x0 | |
| y0, y1 = y1, y0 | |
| } | |
| dx := x1 - x0 | |
| dy := abs(y1 - y0) | |
| err := dx / 2 | |
| y := y0 | |
| ystep := -1 | |
| if y0 < y1 { | |
| ystep = 1 | |
| } | |
| for x := x0; x <= x1; x++ { | |
| if steep { | |
| img.Set(y, x, c) | |
| } else { | |
| img.Set(x, y, c) | |
| } | |
| err -= dy | |
| if err < 0 { | |
| y += ystep | |
| err += dx | |
| } | |
| } | |
| } | |
| func drawObject(img *image.Paletted, w, h int, c color.Color, | |
| drawIdxList []int, meshTris [][]uint, perspVerts [][]float64) { | |
| for _, triIdx := range drawIdxList { | |
| tri := meshTris[triIdx] | |
| i0 := tri[0] | |
| i1 := tri[1] | |
| i2 := tri[2] | |
| p0 := perspVerts[i0] | |
| p1 := perspVerts[i1] | |
| p2 := perspVerts[i2] | |
| drawEdge(img, w, h, c, p0, p1) | |
| drawEdge(img, w, h, c, p0, p2) | |
| drawEdge(img, w, h, c, p1, p2) | |
| } | |
| } | |
| func main() { | |
| const ( | |
| w, h = 240, 240 | |
| numFrames = 360 | |
| ) | |
| // OpenGL coord system: -z goes into the screen | |
| // 8 vertices form corners of the unit cube | |
| var cubeVerts = [][]float64{ | |
| {0.5, 0.5, 0.5}, // front top right 0 | |
| {0.5, -0.5, 0.5}, // front bottom right 1 | |
| {-0.5, -0.5, 0.5}, // front bottom left 2 | |
| {-0.5, 0.5, 0.5}, // front top left 3 | |
| {0.5, 0.5, -0.5}, // back top right 4 | |
| {0.5, -0.5, -0.5}, // back bottom right 5 | |
| {-0.5, -0.5, -0.5}, // back bottom left 6 | |
| {-0.5, 0.5, -0.5}, // back top left 7 | |
| } | |
| var cubeIdxs = [][]uint{ | |
| {0, 1, 3}, // front face 3 0 | |
| {2, 3, 1}, // 2 1 | |
| {3, 2, 7}, // left face 7 3 | |
| {6, 7, 2}, // 6 2 | |
| {4, 5, 0}, // right face 0 4 | |
| {1, 0, 5}, // 1 5 | |
| {4, 0, 7}, // top face 7 4 | |
| {3, 7, 0}, // 3 0 | |
| {1, 5, 2}, // bottom face 2 1 | |
| {6, 2, 5}, // 6 5 | |
| {7, 6, 4}, // back face 4 7 | |
| {5, 4, 6}, // 5 6 | |
| } | |
| var palette = []color.Color{ | |
| color.RGBA{0x00, 0x00, 0x00, 0xff}, color.RGBA{0x00, 0xff, 0x00, 0xff}, | |
| } | |
| images := make([]*image.Paletted, 0, numFrames) | |
| viewPoint := []float64{0, 0, 0, 0} | |
| for frame := 0; frame < numFrames; frame++ { | |
| img := image.NewPaletted(image.Rect(0, 0, w, h), palette) | |
| images = append(images, img) | |
| angle := math.Pi / float64(180) * float64(frame) | |
| mx := getRotXMat4(angle) | |
| my := getRotYMat4(angle) | |
| mz := getRotZMat4(angle) | |
| mt := getTranslMat4(0, 0, -2) | |
| m1 := matMatMult(my, mx) | |
| m2 := matMatMult(mz, m1) | |
| m3 := matMatMult(mt, m2) | |
| worldVerts := projectVerts(m3, cubeVerts[:]) | |
| drawIdxList := cullBackfaces(viewPoint, cubeIdxs, worldVerts) | |
| perspVerts := perspDiv(worldVerts) | |
| drawObject(img, w, h, palette[1], drawIdxList, cubeIdxs, perspVerts) | |
| } | |
| f, err := os.Create("spinningcube.gif") | |
| if err != nil { | |
| fmt.Println(err) | |
| return | |
| } | |
| defer f.Close() | |
| err = gif.EncodeAll(f, &gif.GIF{ | |
| Image: images, | |
| Delay: make([]int, numFrames), | |
| }) | |
| if err != nil { | |
| fmt.Println(err) | |
| return | |
| } | |
| } |
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Result
