Billboarding in Mario Kart style game..?

robertgamble · 2003-09-11T08:51:07

I''m working on a Mario Kart/"Mode 7" style game for the GP32 handheld, and &#106avascript (using &#106avascript as a "testbed" so that I don''t have to keep recompiling and uploading each time I change something). An old &#106avascript version is available here: http://www.elephantsneverforget.co.uk/mode7.asp (wasd to move around), it''s pretty slow but runs great on the GP32 (60fps at 40Mhz). At the moment you can drive around, the graphics look ok and there''s some collision detection. However I can''t work out how to draw cars/trackside objects etc.. At first I was drawing the car with raycasting.. E.g when I draw a pixel on the floor check if the ray coordinates match the car coordinates. But that was very slow, and didn''t seem like the right way of doing it... I was thinking that a better way would be to transform & project the coordinates and then draw the objects as point sprites. But I''m unsure of how to get this "in sync" with whats being drawn by the floorcaster. So what is the best way of doing this? Any help would be greatly appreciated.

Graphics and GPU Programming Programming

Started by robertgamble September 03, 2003 11:17 AM

14 comments, last by robertgamble 20 years, 7 months ago

robertgamble

122

Author

September 11, 2003 04:02 AM

Neoteric, thanks for your example it was very helpful

I''ve got it kind of working now, the only problem is if you move left or right it starts to get distorted. http://www.elephantsneverforget.co.uk/mode7b.htm

I think it''s how I''m working out the angle, how are you working out floor_ray_ang and angstep in your program?

Thanks for your help

Neoteric

122

September 11, 2003 06:11 AM

Ray-ang step is 45 degrees / screen_height.

       /      /     /   o ___________________   <-- line of sight   z \   |  \___|___\________________   <-- intersection on floor        \         \           \     <==90 degree FOV / 2 = 45 / screen_height =                interpolattion_between_hight_&_low_scanlines

I don''t think that''s the problem though, left_ang and right_ang seem to be going wrong. Hope that helps.

robertgamble

122

Author

September 11, 2003 06:41 AM

Doesn''t seem to be anything wrong with left_ang and right_ang, unless I''m missing something..

It almost looks like I''m getting radians & degrees mixed up somewhere, but that shouldn''t happen as I''m using luts for the trig functions...

robertgamble

122

Author

September 11, 2003 07:57 AM

Sorted it, the interpolation increments were being calculated wrong. Shouldn''t be using the absolute value, as it was causing the ray to always go up,right when it shouldn''t.

Thanks for your help with this, it seems faster now and hopefully I''ll get a nice boost in the GP32 version

Neoteric

122

September 11, 2003 08:13 AM

Cool, I''d be interested in seeing it.

robertgamble

122

Author

September 11, 2003 08:51 AM

I''m still having trouble transforming and projecting the coordinates for cars and trackside objects though

this is how did tranform / projection in my proper 3d thing:-

while(curVect				//project, draw and transform this vector				distanceZ=(dspList[curObj].faces[curFace].points[curVect].z+dspList[curObj].z)-this.z;				distanceX=(dspList[curObj].faces[curFace].points[curVect].x+dspList[curObj].x)-this.x;				distanceY=(dspList[curObj].faces[curFace].points[curVect].y+dspList[curObj].y)-this.y;				ntY = parseInt(distanceY*cos[this.xa] - distanceZ*sin[this.xa]) 				ndistance = parseInt(distanceZ*cos[this.xa] + distanceY*sin[this.xa])				distanceY=ntY;				distanceZ=ndistance				ndistance = parseInt(distanceZ*cos[this.ya]) - (distanceX*sin[this.ya])  				ntX = parseInt(distanceX*cos[this.ya]) + (distanceZ*sin[this.ya])				distanceZ=ndistance				distanceX=ntX				ntX = parseInt(distanceX*cos[this.za]) - (distanceY*sin[this.za]) 				ntY = parseInt(distanceY*cos[this.za]) + (distanceX*sin[this.za])				distanceX=ntX;				distanceY=ntY;				distanceZ+=0.001;								tmpvec[curVect]=new vector3D();				tmpvec[curVect].z=distanceZ;				tmpvec[curVect].x=(lens*distanceX/distanceZ)+viewarea.centerx;				tmpvec[curVect].y=viewarea.centery-(lens*distanceY/distanceZ);				curVect++;				}

I think I understand how to transform the coordinates, but not how to project them without a Z coordinate.. bah! Do you know of any simple open source games/demos that do this, it would be nice to see an example..

Billboarding in Mario Kart style game..?

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Billboarding in Mario Kart style game..?

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