Tutorial 9

Textures

In this tutorial we'll learn how to use textures. A texture is a graphic file which is placed in a surface instead of a flat colour. In CsoundAV, you must use .png (Portable Network Graphics) files. Photoshop can export this kind of file, but unfortunately, a file exported by Photoshop is not usable in CsoundAV. You can use a program like Irfanview or Paint Shop Pro to convert the file exported by Photoshop, or use the program to create the file. Irfanview is free, but it does not support the alpha channel. Paint Shop Pro is very inexpensive but very powerful. You might want to check it out at:

www.jasc.com

In this tutorial we'll start seeing the relevance of the order in the rendering chain, as it defines which object is considered the source and which the destination which will define how colours are blended.

You can use any texture you like, or you can use the one I made, which is included in the zip file in the main page.

All headers begin as usual:

-+Y

</CsOptions>

#include "OpenGL.h"

sr=100

kr =100

ksmps=1

nchnls=1

GLfps 30

GLpanel "OpenGL panel", 512, 512

GLpanel_end

FLrun

To load a texture, we use the instruction GLloadTexture. The global variable giTex1 stores a 'handle' value, and can be used later to call this texture. The first parameter as you can see gives the path for the texture. You must adjust the path to your system. Notice that in Csound you should use '/' instead of the usual '\' character to separate pathnames. The next two parameters state how the texture is to be used. First you state the transparency which in this case is $PNG_ALPHA. This means the transparency depends on the alpha channel of the png file. You might want to define a specific colour to be transparent. Check the CsoundAV html help for more paramters. For now we´ll use this value which is the usual value. The next values states whether the texture is to be tiled ($GL_REPEAT) or only drawn once ($GL_CLAMP). In this case we want the texture to repeat (even though the repetitions will not be seen).

giTex1 GLloadTexture "d:/csound/silly.png", $PNG_ALPHA , $GL_REPEAT

Loading of textures must always be done at initialization so we need to place the following line after any loading of textures.

GLinsert_i $GL_INIT

glMatrixMode $GL_PROJECTION

glLoadIdentity

gluPerspective 60,0.1,100

glMatrixMode $GL_MODELVIEW

glEnable $GL_BLEND

;glEnable $GL_DEPTH_TEST

For blending to work as we intend the depth test must be disabled. I leave this comment line so you can see what happens if we leave depth test on.

glBlendFunc $GL_SRC_ALPHA,$GL_ONE_MINUS_SRC_ALPHA

We use the standard blending function.

glEnable $GL_TEXTURE_2D

We enable the use of 2D textures with the previous command.

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

The rest of the headers go as usual. Now to our instrument.

instr 1

idisp = p4

t1 GLoscil 0.5,360,gisine

We create a sine wave oscillator which will later control the z position of our object.

glLoadIdentity

glBindTexture giTex1

Before drawing a textured object, we must tell the engine which texture to use. This is done with glBindTexture, which has only one parameter which is the 'handle' value of the texture.

glTranslate p4,p4/2,(-t1) -5

The x and y position is defined by p-field 4 and the z position is variable according to the oscillator created above.

GLtexSquare 1, 1,0,0,0,0,1,0,0

the instruction GLtexSquare creates a textured square. The first parameter gives the dimensions of the sides of the square. The next four pairs of parameters give the texture coordinates, starting from the lower right hand corner, and going counterclockwise. In this case the texture occupies the whole square created. These coordinates are 'normalized', in the sense that they are independent of the size of the square created, and always assume a square of size 1.

GLinsert 1.5

endin

</CsInstruments>

Now we draw the squares.

i1 1 60 2

i1 4 60 1

i1 8 60 0

i1 10 60 -1

i1 12 60 -2

</CsScore>

</CsoundSynthesizer>

That's it. I've included in the csd other examples (commented out) of texture mapping in the zip file that contains the tutorials. You might want to comment them out and see the results.

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