Texture mapping

From 17dc0febb17888015be1e4ad1ed4b096a4909865 Mon Sep 17 00:00:00 2001 From: Travis CI Date: Thu, 19 Mar 2015 20:12:11 +0000 Subject: Gem 206d71791bc3642e8c5391a4c59c30ba7411fab8 osx/i386 built 'master:206d71791bc3642e8c5391a4c59c30ba7411fab8' for osx/i386 --- Gem/manual/Texture.html | 126 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 126 insertions(+) create mode 100644 Gem/manual/Texture.html (limited to 'Gem/manual/Texture.html') diff --git a/Gem/manual/Texture.html b/Gem/manual/Texture.html new file mode 100644 index 0000000..1de889c --- /dev/null +++ b/Gem/manual/Texture.html @@ -0,0 +1,126 @@ + + + + + + + Texture mapping + + + + +

+Texture Mapping

+Texture mapping is the act of applying +pixel data to a geometric object. In GEM, this is achieved with the +[pix_texture] +object. It is important to understand that the +[pix_texture] +object merely sets the pix as the current texture. It does not do +any rendering! You need to use a geo object which does texture mapping. +All of the basic geo objects can texture map, such as [square] or +[sphere]. +

A simple example of texture mapping is the following patch: +

+ +

This patch can be found at 07.texture/01.texture.pd. Change +the number box connected to the rotate object to see what a texture map +on a cube looks like. +

The [pix_image] object loads in the fractal image file. The +[pix_texture] +object says that the pix data should be used as a texture map. Notice +that this is different than the previous manual section when we used the +[pix_draw] object. The final object in the chain is the [cube] +object. Because we have enabled texture mapping with the [pix_texture] +object, the cube takes the pix data and applies it to the geometry. +

Texture mapping can be used with any GEM object. In the previous +manual section, you saw how to load in pix data with a variety of objects, +including [pix_multiimage] and [pix_video]. All of these +objects can be used with the [pix_texture] object. +

Because the pix data is applied to geometry, you can move, rotate, and +scale the image. This is extremely useful on the [square] object. +Instead of doing a one-to-one pixel mapping as occurs with the [pix_draw] +object, you can resize and reshape the image. +

OpenGL originally required that images must have dimensions that are power-of-2, such as 64, 128, or 256. This restriction has been released with recent gfx-cards +(like some radeon/nvidia products). +However, if the width or height of an image is not a power of two, +then the [pix_texture] object will take care of this, +and still render it (depending on you hardware with some tricks). +You can thus texture images of any size, but since this is based on tricking +the texture-coordinates, [pix_coordinate] might not give the wanted result any more. +

The example patch 07.texture/02.moveImages.pd is a much more complex +patch which uses alpha blending to create a transparent object, in this +case, the dancer. Make sure to turn on the rotation with the [metro] +object. +

People have been asking how textures are handled in GEM. Here +is a long explanation from an email which I wrote. +

Here is how textures are dealt with under OpenGL and hardware +accelerators. This can obviously change in the future, but right +now, I am fairly certain that the info is correct (I make games in my day +job, so I have vested interest in this :-) +

The amount of memory (VRAM) on the card (12mb for Voodoo2, +16mb for TNT, 64mb for GeForce2, etc) is used for both textures (TRAM) +and frame buffer space. If you have a large rendering window, like +1600x1200, it will take up 1600x1200x4x3 in 32-bit mode with double buffering +and a Z buffer (or 23mb). Most people run at TV resolution, like +NTSC, so it takes 640x480x4x3 = 3.7mb All of the space left +is for textures onboard the card (FYI, if you have heard that people are +having problems with the PlayStation2, notice that it only has 4mb of VRAM...not +much onboard texture space, huh? :-) Thankfully it has an extremely +fast DMA bus) +

Sooo, when GEM "creates" a texture, it immediately tries +to send the texture to the card, which uses some of the left over space +in the VRAM. If you had a 640x480 window on a Voodoo2, you have ~8mb +of texture space left over. On a GeForce2, ~60mb. The problem +is what happens if you want more textures than can fit into TRAM. +OpenGL requires that the video drivers deal with the problem, so GEM doesn't +care too much (more about this later). +

In most cases, the drivers cache the textures in main memory +and if a texture is requested for rendering and it isn't resident on the +card, it will download it. If you have AGP, then this is pretty quick, +although none of 3dfx cards really take advantage of this (ie, those cards +are about the same speed as the PCI bus). So depending on the number +of textures, and how complex the scene is, you might be able to display +more textures than you have TRAM. +

One slowdown that can happen with GEM is that it makes a +copy of the image before sending it down the chain of objects. If +you are constantly changing images with a pix_multiimage, this can be a +performance hit, but you can modify the actual pixel data with the pix +objects. The pixels aren't sent to the graphics card until the pix_texture +object is reached. +

GEM tries to help with this with a few objects. pix_imageInPlace +acts much the same as pix_multiimage, but it downloads _every_ image in +the sequence to the card when a download message is recieved. It +also immediately turns on texturing, instead of making a copy (ie, you +don't need a pix_texture object). Much faster, but not as flexible. +pix_movie does much the same thing. It sends the pixel data without +copying it if there is a new frame to display. +

The entire pix system uses a caching system so that the copying +and processing only occurs if something actually changes. For example, +if you had a pix_threshold object, it would only process when rendering +started...and every time that the values actually changed. You can +use pix_buf to isolate parts which don't change from those that do, but +it involves another copy. +

On the Voodoo2, the hardware itself limits textures to 256x256...this +will never change. The newest Voodoo5 boards have a higher texture +size. +

If you load the _exact_ same image (this means the exact +same file/path name), then the pix_image has a cache system which means +that it is only loaded into the +
computers memory once. However, each pix_image still sends +its own copy down to the gfx card. +

You could use a single [pix_image]/[pix_texture] with [separator] +to do this...I have done it a lot in the past. +

The reason that [pix_image] doesn't share the actual texture +data is that you can modify the pixel data with other pix objects...[pix_image] +doesn't actually send the texture data to the gfx card, [pix_texture] does. +

[return] +
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