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12
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1 When an object change it's size, position, or components inside it,
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2 other objects overlaid with the object in old or new positions should
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3 be re-drawed. The place that the object is resident in old or new
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4 position should be cleared before re-drawing. We need a system
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5 to determine and track effected by the change of an object.
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6
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7 The graphics are grouped into groups in tree-hierachy. One group
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8 can be part of another group. When a group's transformation matrix
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9 is chagned, all child groups should be affected. All it's members
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10 should also be re-drawed. All members of a group been changed are
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11 linked into update list in their order. The one more close to
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12 tree root is more earier in the list.
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13
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14 Transformations can only apply to groups. A tree of coord_t is
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15 maintained to model relationships of groups. Coord_t is coordination,
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16 a transfromation from user space to upper level's space or devcie space.
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17
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18 coord_t must know graphics in respective group. Once transformation
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19 matrix of a coord_t object changed, it can ask members to
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20 re-drawed them-self.
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21
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22 Changes of the transformation of a coord_t should be propagated to
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23 child coord_t objects/groups.
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24
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