android camera intent - Page 408

Android: How can i make my page slide as the user slides finger on the screen?

- by Maxood

How can i make my page slide as the user slides finger on the screen in android? Any example code?

projection / view matrix: the object is bigger than it should and depth does not affect vertices

I'm currently trying to write a C 3D software rendering engine from scratch just for fun and to have an insight on what OpenGL does behind the scene and what 90's programmers had to do on DOS. I have written my own matrix library and tested it without noticing any issues, but when I tried projecting the vertices of a simple 2x2 cube at 0,0 as seen by a basic camera at 0,0,10, the cube seems to appear way bigger than the application's window. If I scale the vertices' coordinates down by 8 times I can see a proper cube centered on the screen. This cube doesn't seem to be in perspective: wheen seen from the front, the back vertices pe rfectly overlap with the front ones, so I'm quite sure it's not correct. this is how I create the view and projection matrices (vec4_initd initializes the vectors with w=0, vec4_initw initializes the vectors with w=1): void mat4_lookatlh(mat4 *m, const vec4 *pos, const vec4 *target, const vec4 *updirection) { vec4 fwd, right, up; // fwd = norm(pos - target) fwd = *target; vec4_sub(&fwd, pos); vec4_norm(&fwd); // right = norm(cross(updirection, fwd)) vec4_cross(updirection, &fwd, &right); vec4_norm(&right); // up = cross(right, forward) vec4_cross(&fwd, &right, &up); // orientation and translation matrices combined vec4_initd(&m->a, right.x, up.x, fwd.x); vec4_initd(&m->b, right.y, up.y, fwd.y); vec4_initd(&m->c, right.z, up.z, fwd.z); vec4_initw(&m->d, -vec4_dot(&right, pos), -vec4_dot(&up, pos), -vec4_dot(&fwd, pos)); } void mat4_perspectivefovrh(mat4 *m, float fovdegrees, float aspectratio, float near, float far) { float h = 1.f / tanf(ftoradians(fovdegrees / 2.f)); float w = h / aspectratio; vec4_initd(&m->a, w, 0.f, 0.f); vec4_initd(&m->b, 0.f, h, 0.f); vec4_initw(&m->c, 0.f, 0.f, -far / (near - far)); vec4_initd(&m->d, 0.f, 0.f, (near * far) / (near - far)); } this is how I project my vertices: void device_project(device *d, const vec4 *coord, const mat4 *transform, int *projx, int *projy) { vec4 result; mat4_mul(transform, coord, &result); *projx = result.x * d->w + d->w / 2; *projy = result.y * d->h + d->h / 2; } void device_rendervertices(device *d, const camera *camera, const mesh meshes[], int nmeshes, const rgba *color) { int i, j; mat4 view, projection, world, transform, projview; mat4 translation, rotx, roty, rotz, transrotz, transrotzy; int projx, projy; // vec4_unity = (0.f, 1.f, 0.f, 0.f) mat4_lookatlh(&view, &camera->pos, &camera->target, &vec4_unity); mat4_perspectivefovrh(&projection, 45.f, (float)d->w / (float)d->h, 0.1f, 1.f); for (i = 0; i < nmeshes; i++) { // world matrix = translation * rotz * roty * rotx mat4_translatev(&translation, meshes[i].pos); mat4_rotatex(&rotx, ftoradians(meshes[i].rotx)); mat4_rotatey(&roty, ftoradians(meshes[i].roty)); mat4_rotatez(&rotz, ftoradians(meshes[i].rotz)); mat4_mulm(&translation, &rotz, &transrotz); // transrotz = translation * rotz mat4_mulm(&transrotz, &roty, &transrotzy); // transrotzy = transrotz * roty = translation * rotz * roty mat4_mulm(&transrotzy, &rotx, &world); // world = transrotzy * rotx = translation * rotz * roty * rotx // transform matrix mat4_mulm(&projection, &view, &projview); // projview = projection * view mat4_mulm(&projview, &world, &transform); // transform = projview * world = projection * view * world for (j = 0; j < meshes[i].nvertices; j++) { device_project(d, &meshes[i].vertices[j], &transform, &projx, &projy); device_putpixel(d, projx, projy, color); } } } this is how the cube and camera are initialized: // test mesh cube = &meshlist[0]; mesh_init(cube, "Cube", 8); cube->rotx = 0.f; cube->roty = 0.f; cube->rotz = 0.f; vec4_initw(&cube->pos, 0.f, 0.f, 0.f); vec4_initw(&cube->vertices[0], -1.f, 1.f, 1.f); vec4_initw(&cube->vertices[1], 1.f, 1.f, 1.f); vec4_initw(&cube->vertices[2], -1.f, -1.f, 1.f); vec4_initw(&cube->vertices[3], -1.f, -1.f, -1.f); vec4_initw(&cube->vertices[4], -1.f, 1.f, -1.f); vec4_initw(&cube->vertices[5], 1.f, 1.f, -1.f); vec4_initw(&cube->vertices[6], 1.f, -1.f, 1.f); vec4_initw(&cube->vertices[7], 1.f, -1.f, -1.f); // main camera vec4_initw(&maincamera.pos, 0.f, 0.f, 10.f); maincamera.target = vec4_zerow; and, just to be sure, this is how I compute matrix multiplications: void mat4_mul(const mat4 *m, const vec4 *va, vec4 *vb) { vb->x = m->a.x * va->x + m->b.x * va->y + m->c.x * va->z + m->d.x * va->w; vb->y = m->a.y * va->x + m->b.y * va->y + m->c.y * va->z + m->d.y * va->w; vb->z = m->a.z * va->x + m->b.z * va->y + m->c.z * va->z + m->d.z * va->w; vb->w = m->a.w * va->x + m->b.w * va->y + m->c.w * va->z + m->d.w * va->w; } void mat4_mulm(const mat4 *ma, const mat4 *mb, mat4 *mc) { mat4_mul(ma, &mb->a, &mc->a); mat4_mul(ma, &mb->b, &mc->b); mat4_mul(ma, &mb->c, &mc->c); mat4_mul(ma, &mb->d, &mc->d); }

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