OpenGL Help??

BlitzMax Forums/BlitzMax Programming/OpenGL Help??

hyphz

(Posted 2004) [#1]

Ok, so I have the following code:

Import brl.BlitzGL
Import pub.OpenGL

bglCreateContext 800,600,16,0,BGL_BACKBUFFER | BGL_DEPTHBUFFER

glShadeModel GL_SMOOTH
glClearColor 0.0,0.0,0.0,0.0

val = 0

While Not KeyDown(KEY_ESCAPE)

glMatrixMode GL_PROJECTION
glLoadIdentity
gluPerspective 45,800/600,0.1,100
glMatrixMode GL_MODELVIEW
glLoadIdentity
glClearDepth 0.0

glViewPort 0,0,800,600

glEnable(GL_DEPTH_TEST)
glDepthFunc(GL_LEQUAL)
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST)
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

glRotatef val,0,0,0
val = val + 1
glBegin GL_QUADS
glVertex2f -1,1
glVertex2f 1,1
glVertex2f 1,-1
glVertex2f -1,-1
glEnd
FlushMem
bglSwapBuffers

Wend

End

But it seems to produce a blank window. Further, when I previously tried it without the rotation, it did produce a quad but it was rectangular rather than square, suggesting that the aspect ratio was wrong.

I've tried re-arranging all of the initialisation stuff several times and copying the order out of the OpenGL example included with blitzMax but it still refuses to show anything. Can anyone give me a clue what's going on?

AntonyWells

(Posted 2004) [#2]

Rotate is axis based, i.e

glRotateF Angle,PitchBit,YawBit,RollBit.

glRotateF Roll,0,0,1
glRotateF Yaw,0,1,0
glRotateF Pitch,1,0,0,

also for 2d stuff, you're better off using orothogonal projection,

	glViewport 0, 0, dWidth,dHeight
	glMatrixMode gl_projection
	glLoadIdentity()
	gluortho2d(0.0, dWidth, 0.0, dHeight )
	glMatrixMode gl_modelview
	glLoadIdentity

then you can specify verts in pixel space.

hyphz

(Posted 2004) [#3]

Well, I tried changing those but still got nothing, so I pulled the rotate altogether, but it still just comes up blank:

Import brl.BlitzGL
Import pub.OpenGL

bglCreateContext 800,600,16,0,BGL_BACKBUFFER | BGL_DEPTHBUFFER

glShadeModel GL_SMOOTH
glClearColor 0.0,0.0,0.0,0.0

val = 0

While Not KeyDown(KEY_ESCAPE)

glViewport 0, 0, 800,600
glMatrixMode gl_projection
glLoadIdentity
gluortho2d 0.0, 800, 0.0, 600
glMatrixMode gl_modelview
glLoadIdentity

glClearDepth 0.0

glEnable(GL_DEPTH_TEST)
glDepthFunc(GL_LEQUAL)
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST)
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

'glRotatef val,1,0,0
glColor3f 1,1,1

glBegin GL_QUADS
glVertex2f -1,100
glVertex2f 100,100
glVertex2f 100,-1
glVertex2f -1,-1
glEnd
FlushMem
bglSwapBuffers

Wend

End

Extron

(Posted 2004) [#4]

Copy/paste your code don't work.

Try this :

Import brl.BlitzGL
Import pub.OpenGL

val:Float=0.0

bglCreateContext (800, 600, 32, 0, BGL_BACKBUFFER | BGL_DEPTHBUFFER)
bglSetSwapInterval(1)
InitGl()
While Not KeyHit( KEY_ESCAPE )
	' Clear The Screen And The Depth Buffer
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
	' Reset The Current Modelview Matrix	
	glLoadIdentity()
	glColor3f 1.0,1.0,1.0
	glRotatef val,1,0,0
	glBegin GL_QUADS
		glVertex2f -1.0,100.0
		glVertex2f 100.0,100.0
		glVertex2f 100.0,-1.0
		glVertex2f -1.0,-1.0
	glEnd
	val:+0.1
	FlushMem
	bglSwapBuffers
Wend
End

Function InitGl()
	' Enable Smooth Shading
	glShadeModel(GL_SMOOTH)
	' Black Background
	glClearColor(0.0, 0.0, 0.0, 0.5)
	' Depth Buffer Setup
	glClearDepth(1.0)
	' Enables Depth Testing
	glEnable(GL_DEPTH_TEST)
	' The Type Of Depth Testing To Do
	glDepthFunc(GL_LEQUAL)
	' Really Nice Perspective Calculations
	glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST)

	' Set viewport
	glViewport(0,0,800,600)
	' Select The Projection Matrix
	glMatrixMode(GL_PROJECTION)
	' Reset The Projection Matrix
	glLoadIdentity()
	gluortho2d(0.0, 800, 0.0, 600)
	' Select The Modelview Matrix
	glMatrixMode(GL_MODELVIEW)
	' Reset The Modelview Matrix
	glLoadIdentity()
End Function

teamonkey

(Posted 2004) [#5]

hyphz - Of all of these lines in your code:

glViewport 0, 0, 800,600
glMatrixMode gl_projection
glLoadIdentity
gluortho2d 0.0, 800, 0.0, 600
glMatrixMode gl_modelview
glLoadIdentity

glClearDepth 0.0

glEnable(GL_DEPTH_TEST)
glDepthFunc(GL_LEQUAL)
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST)

Only the second glLoadIdentity should be in the main loop.