Tutorial 5

glScale and rotation

This tutorial doesn´t introduce many new concepts, but expands on instructions previously studied. The new instruction introduced in this tutorial is glScale . This instruction 'scales' our reference axis. It is a cumulative transformation like others we've seen in the sense that all transformations after it are affected by the scaling, until a new glLoadIdentity appears to clear transformations. For example if after scaling the reference axis to twice the size and then translating 1 unit, what will happen is actually a translation of two units, since we are translating one unit on a scaled axis. The other thing that is played around with is colour values (look at the score) and rotation. See how simple rotations can create nice 3D effects.

-+Y

</CsOptions>

#include "OpenGL.h"

sr=100

kr =100

ksmps=1

nchnls=1

GLfps 30

GLpanel "OpenGL panel", 512, 512

GLpanel_end

FLrun

glMatrixMode $GL_PROJECTION

glLoadIdentity

gluPerspective 60,0.1,100

glMatrixMode $GL_MODELVIEW

GLinsert_i $GL_NOT_VALID

glClear $GL_COLOR_BUFFER_BIT + $GL_DEPTH_BUFFER_BIT

GLinsert_i 1.1

gisine ftgen 1,0,1024,10,1

All our usual headers.

instr 2

ired = p4

igreen = p5

iblue = p6

ix = p7

iy = p8

glLoadIdentity

tsize GLoscil 1,360,1

trot1 GLoscil 1,300,1

Instrument 2 is very similar (and based) on instrument 2 from the previous tutorial. P-field assignments are a little different, and we will use to independent oscillators to control rotation and size. Notice the frequency difference in both.

glTranslate ix,iy,-6

glRotate (trot1*360),1,0,1

Notice that we rotate around the x and the z axis simultaneously, which produces a strong 3D rotation.

glColor ired,igreen,iblue,1

glScale (tsize*3) , (tsize*3) ,(tsize*3)

The glScale instruction has three values which indicate the scaling of each axis. If the values are equal, the relative shape remains the same. If they are different, the aspect ratio is changed and even rotations will behave strangely. What will happen here is that the objects will grow from 0 size to 3 times the size, back to 0 and then when the negative part of the oscillator comes, the shape is drawn in the opposite direction. This will be clearer when you run the program.

glLineWidth 6

This instruction determines how thick a line will be rendered. Useful when drawing lines instead of filled polygons, as below.

glBegin $GL_LINE_LOOP

Notice that this time instead of $GL_QUADS we've used $GL_LINE_LOOP. This creates lines connecting every point, instead of a filled polygon. Notice that a line is added between the last vertex and the first, closing the loop.

glVertex3 0,0,0

glVertex3 1,0,0

glVertex3 1,1,0

glVertex3 0,1,0

glEnd

GLinsert 1.5

endin

</CsInstruments>

i 2 2 38 1 0 0 1 -1

i 2 3 37 0.8 0.2 0 0.8 -0.8

i 2 4 36 0.6 0.4 0 0.6 -0.6

i 2 5 35 0.4 0.6 0 0.4 -0.4

i 2 6 34 0.2 0.8 0 0.2 -0.2

i 2 7 33 0 1 0 0 0

i 2 8 32 0 0.8 0.2 -0.2 0.2

i 2 9 31 0 0.6 0.4 -0.4 0

i 2 10 30 0 0.4 0.6 -0.6 0

i 2 11 29 0 0.2 0.8 -0.8 0

i 2 12 28 0 0 1 -1 0

i 2 13 27 0.2 0 0.8 -1.2 0

i 2 14 26 0.4 0 0.6 -1.4 0

Notice how the colour is gradually changing and how this reflects on the colour of the objects.

</CsScore>

</CsoundSynthesizer>

As I said before this tutorial doesn't introduce too many new concepts but shows other uses of the instructions we've seen in previous tutorials. It also looks a lot nicer because it moves more 'unexpectedly'. As always experiment a lot changing values and adding whatever you come up with to see the results.