Beginner-questions

BlitzMax Forums/OpenGL Module/Beginner-questions

eindbaas

(Posted 2006) [#1]

Ok, i editted my post here. I got some things working, even though i don't exactly know why certain things occur as they do. I'm just moving along, hoping i'll find them out later on.

Anyway: i'm trying to figure out how to have my quads get opacity. i read tutorials, examples but can't find out why i don't get any results in that direction.

i used
glEnable(GL_BLEND)
glColor4f(1.0,0,0,0.21)
glBlendFunc (GL_SRC_ALPHA, L_ONE_MINUS_SRC_ALPHA)

Is there more i should take care of before any alpha on my quads will work?

(apologies for the bad title - can't seem to fix that anymore)

Global ScreenWidth:Int=800
Global ScreenHeight:Int=600
Global ScreenDepth:Int=16

GLGraphics ScreenWidth,ScreenHeight


init()

Global pos_x# = 0
Global pos_y# = 0
Global pos_z# = 0

Global objectList:TList=CreateList()


createCubes(10)


While Not KeyHit( KEY_ESCAPE )

	glClear GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT 
	glLoadIdentity
	
	checkKeys()


	' eigen positie 
	xtrans# = -pos_x#
	ytrans# = -pos_y#
	ztrans# = -pos_z#		
	
	
	glTranslatef xtrans#, ytrans#, ztrans#

	For current_cube:cube = EachIn objectList

		px# = current_cube.posX#
		py# = current_cube.posY#
		pz# = current_cube.posZ#

		rx# = current_cube.rotX#
		ry# = current_cube.rotY#
		rz# = current_cube.rotZ#
		

		glPushMatrix()
		glTranslatef px#,py#,pz#
		glRotatef rx#,1,0,0

		drawCube(0.5)			
		glPopMatrix()		
		
		current_cube.rotX# = current_cube.rotX# + 4
	Next	
	
	Flip

Wend

Function init()
	glClearColor(0.9, 0.9, 0.9, 0.0)
'	glClearDepth 1.0
'	glDepthFunc(GL_LESS)
'	glDisable(GL_DEPTH_TEST)
	glEnable(GL_BLEND)
'	glShadeModel(GL_SMOOTH)
	glViewport(0,0,ScreenWidth,ScreenHeight)
	glMatrixMode(GL_PROJECTION)
	glLoadIdentity()
	gluPerspective(45.0,Float(ScreenWidth)/Float(ScreenHeight),1.0,100.0)
	glMatrixMode(GL_MODELVIEW)
End Function

Function checkKeys()

	speed# = .1
	
	' MOVEMENT
	
	If KeyDown (KEY_UP)
		pos_z# = pos_z# - speed#
	End If
	If KeyDown (KEY_DOWN)
		pos_z# = pos_z# + speed#
	End If
	If KeyDown (KEY_LEFT)
		pos_x# = pos_x# - speed#
	End If
	If KeyDown (KEY_RIGHT)
		pos_x# = pos_x# + speed#
	End If
	If KeyDown (KEY_Q)
		pos_y# = pos_y# + speed#
	End If
	If KeyDown (KEY_A)
		pos_y# = pos_y# - speed#
	End If
	


	'DebugLog (pos_x#+"  "+pos_y#+"  "+pos_z#)
End Function


Function drawCube(size#)

	glBegin GL_QUADS
	
		halve# = size# / 2.0
		glColor4f(1.0,0,0,0.21)
		glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
		
	
		'achterkant
		glVertex3f -halve#, halve#, -halve#					'Top Left
		glVertex3f  halve#, halve#, -halve#					'Top Right
		glVertex3f  halve#,-halve#, -halve#				'Bottom Right
		glVertex3f -halve#,-halve#, -halve#					'Bottom Left

		'voorkant
		glVertex3f -halve#, halve#, halve#					'Top Left
		glVertex3f  halve#, halve#, halve#					'Top Right
		glVertex3f  halve#,-halve#, halve#				'Bottom Right
		glVertex3f -halve#,-halve#, halve#					'Bottom Left


		'linkerkant
		glVertex3f -halve#, halve#, halve#					'Top Left
		glVertex3f -halve#,-halve#, halve#
		glVertex3f -halve#,-halve#, -halve#				'Bottom Left
		glVertex3f -halve#, halve#, -halve#				'Bottom Right
		
		'rechterkant
		glVertex3f halve#, halve#, halve#					'Top Left
		glVertex3f halve#,-halve#, halve#
		glVertex3f halve#,-halve#, -halve#				'Bottom Left
		glVertex3f halve#, halve#, -halve#				'Bottom Right
		
		'onderkant
		glVertex3f -halve#,-halve#, halve#					'Top Left
		glVertex3f -halve#,-halve#, -halve#
		glVertex3f halve#,-halve#, -halve#				'Bottom Left
		glVertex3f halve#,-halve#, halve#				'Bottom Right
		
		'bovenkant
		glVertex3f -halve#,halve#, halve#					'Top Left
		glVertex3f -halve#,halve#, -halve#
		glVertex3f halve#,halve#, -halve#				'Bottom Left
		glVertex3f halve#,halve#, halve#				'Bottom Right
		
	glEnd
End Function


Function createCubes(num%)

	For n=1 To num%
		div# = .5
	
		obj:cube = New cube
'		obj.posX# = Rnd(-div#,div#)
'		obj.posY# = Rnd(0,div#)
'		obj.posZ# = Rnd(-div#,0)
		
		obj.posX# = n
		obj.posY# = 0
		obj.posZ# = -6
		
		obj.rotX# = 0.4
		obj.rotY# = 0.0
		obj.rotZ# = 0.0			


		ListAddLast objectList, obj
	
		DebugLog CountList(objectList)
	Next
End Function

Type cube
	Field posX#
	Field posY#	
	Field posZ#	
	
	Field rotX#
	Field rotY#	
	Field rotZ#	
	
End Type

LeisureSuitLurie

(Posted 2006) [#2]

You can't call GLBlendFunc inside a GLBegin...GLEnd block. Move it above GLBegin and it works.

eindbaas

(Posted 2006) [#3]

thank you, that works indeed.

my alpha-values have some effect now, although i'm not getting the results i wanted. how would i get a cube that you can see through slightly? i get a 1-color-solid version of the cube, but expected for example to be able to see faces at the rear of the cube (by looking through the front ones).

LeisureSuitLurie

(Posted 2006) [#4]

Alpha ranges from zero to 1. Keep in mind two of the faces (at least) will overlap and make the cube seem less transparent. Try drawing a busy background behind it.

Cruis.In

(Posted 2006) [#5]

I'd like to be able to use this for zooming in my project. But I have a bit of difficulty understanding certain things for opengl.

if I set my graphics with GLGraphics, it returns null object for the first image it tries to load. Setting it back is fine.

If i use this code as is and I load and draw an image in it, it returns null object when I run it, if i change glgraphics to graphics it works and it draws a black screen with my image only.

ive set my graphics driver to opengl in my project, why won't this stuff work with graphics. and why when i use GLgraphics in my app does it not work.

can this work to tanslate the z of normal drawn images in max? or in tanslatef on the z coordinate only works because he is using opengl cubes...

and i think someone said somewhere that max images are quads, so they should be able to go in and out of the screen right?

gltanslatef is what i need, but i have no idea how to implement it, in the function i use in my project i call all the right things like the glprojection, glmodelview, glloadidentity, but my graphics just flicks right off the screen when i zoom.

ImaginaryHuman

(Posted 2006) [#6]

You can use glColor4ub if you want to use values 0..255 without having to think what it is as a decimal of 1

Cruis.In

(Posted 2006) [#7]

that solves the problem i spoke of? :)