Method and apparatus for three-dimensional graphics, and computer product

1. A graphic apparatus that draws an object three-dimensionally using a level plane and a height-axis perpendicular to the level plane, comprising:

a receiving unit that receives first vertex data identifying a position of a first top surface of a first object on the level plane and second vertex data identifying a position of a second top surface of a second object on the level plane, wherein the first vertex data is different from the second vertex data;

a calculating unit that calculates a modulation coefficient of luminance for the first top surface based on a normal vector for the first top surface and a light-source vector indicating a direction of a light source on the level plane; and

a drawing unit that draws the first top surface using the first vertex data and the modulation coefficient, and the second top surface of the second object using the second vertex data and the modulation coefficient.

2. The graphic apparatus according to claim 1 , further comprising:

a setting unit that sets normal vectors on the level plane respectively for side surfaces of the object based on the vertex data.

3. The graphic apparatus according to claim 2 , wherein

the setting unit, based on the normal vectors respectively for two adjacent side surfaces of the object, sets a normal vector on the level plane for a ridge line between the adjacent side surfaces,

the calculating unit calculates a modulation coefficient of luminance for the adjacent side surfaces based on the normal vector for the ridge line, and

the drawing unit draws the adjacent side surfaces using the vertex data and the modulation coefficient of luminance for the adjacent side surfaces.

4. The graphic apparatus according to claim 2 , further comprising

a determining unit that determines, based on two pieces of vertex data identifying a side surface and a sight-line vector indicating a direction of a sight line on the level plane, whether the side surface is opposed to the direction of the sight line, wherein

the calculating unit calculates a modulation coefficient of luminance for the side surface based on a determination result by the determining unit.

5. The graphic apparatus according to claim 4 , wherein the determining unit determines whether the side surface is opposed to the direction of the sight line based on a sign of an inner product of a normal vector for the side surface and the sight-line vector.

6. The graphic apparatus according to claim 4 , wherein the drawing unit draws the side surface with a hidden surface removal method.

7. The graphic apparatus according to claim 2 , wherein

the setting unit, based on the vertex data, sets the normal vectors to be opposed to a sight-line vector indicating a direction of a sight line on the level plane, and the drawing unit draws the side surfaces with a hidden surface removal method.

8. A graphic method of drawing an object three-dimensionally using a level plane and a height-axis perpendicular to the level plane, comprising:

receiving, by at least one processor, first vertex data identifying a position of a first top surface of a first object on the level plane and second vertex data identifying a position of a second top surface of a second object on the level plane, wherein the first vertex data is different from the second vertex data;

calculating a modulation coefficient of luminance for the first top surface based on a normal vector for the first top surface and a light-source vector indicating a direction of a light source on the level plane; and

drawing the first top surface using the first vertex data and the modulation coefficient, and the second top surface of the second object using the second vertex data and the modulation coefficient.

9. The graphic method plane according to claim 8 , further comprising:

setting normal vectors on the level plane respectively for side surfaces of the object based on the vertex data.

10. A non-transitory recording medium that stores therein a graphic program for drawing an object three-dimensionally using a level plane and a height-axis perpendicular to the level plane, the graphic program causing a computer to execute:

receiving first vertex data identifying a position of a first top surface of a first object on the level plane and second vertex data identifying a position of a second top surface of a second object on the level plane wherein, the first vertex data is different from the second vertex data;

calculating a modulation coefficient of luminance for the first top surface based on a normal vector for the first top surface and a light-source vector indicating a direction of a light source on the level plane; and

drawing the first top surface using the first vertex data and the modulation coefficient, and the second top surface of the second object using the second vertex data and the modulation coefficient.

11. The non-transitory recording medium according to claim 10 , the graphic program causing a computer to execute:

setting normal vectors on the level plane respectively for side surfaces of the object based on the vertex data.