Hi,

is there a way to create a bitmap and use it temporarly to draw some graphics on it using MiniGL (as a buffer) ?
Didn't find how to ~

Kindest Regards,
AmiDARK

@AmiDARK

Can you not just use glReadPixels after creating the image?

Then just run through the data and save it as a bitmap...

Or am I misunderstanding your request?

Last edited by BinoX on 30-May-2011 at 04:09 PM.

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@BinoX
No.

I need to have an alternate RGB buffer and have the capability to switch from one RGB buffer to another one.

Regards,
AmiDARK

@AmiDARK

You can allocate your bitmaps with graphics library then create a minigl context with private buffers. ie one where you provide the buffers yopurself, and no window is opened directly by minigl.

m_frontBuffer = m_IGraphics->AllocBitMap(w,h,8,BMF_MINPLANES | BMF_DISPLAYABLE,m_window->RPort->BitMap);      
m_backBuffer = m_IGraphics->AllocBitMap(w,h,8,BMF_MINPLANES | BMF_DISPLAYABLE,m_window->RPort->BitMap);

               if(!(m_mglcontext = (struct GLContextIFace *)IMiniGL->CreateContextTags(
                                             MGLCC_PrivateBuffers, 2,
                                             MGLCC_FrontBuffer,m_frontBuffer,
                                             MGLCC_BackBuffer,m_backBuffer,
                                             MGLCC_Buffers,  2,             /* double buffered */
                                             MGLCC_PixelDepth,       16, 
                                             MGLCC_StencilBuffer,    TRUE,
                                             MGLCC_VertexBufferSize, 1 << 17,
                                             MGLCC_FBDirtyHook,fbdirtyhook,
                                             MGLCC_FBDirtyHookData,this ,
                                             TAG_DONE)))
        {

Last edited by broadblues on 30-May-2011 at 08:26 PM.

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@broadblues
Your idea is really interesting.

However, I don't need double buffer .. single buffer is enough... Drawn mades in that buffer will never be directly displayed.

Sample :
1. Create virtual bitmap
2. Load a big image
3. Paste the image in the buffer
4. Create small images from the big images
5. Close the bitmap

I think that I have resumed things.
Your sample should be enough to give me a direction to search to.

Do you think I can change context even if main display is initialisez using GLUT ?

Thank you
@ +
AmiDARK

Last edited by AmiDARK on 30-May-2011 at 09:28 PM.

@AmiDARK

C'est la vie.

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@AmiDARK

Broadblues is english and I don't think he reads french

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@elwood
Just edited my previous post.

Sometimes brain act *so fast* that I don't mind to what I do :p
Fixed now :)

Regards,
AmiDARK

Last edited by AmiDARK on 30-May-2011 at 09:29 PM.
Last edited by AmiDARK on 30-May-2011 at 09:29 PM.

@AmiDARK

Arf, You thought you were on Amiga-NG, didn't you ?

@Broadblues

He finds your idea very interesting but he doesn't need double buffer, only one buffer sincegraphics drawed in this bitmap would never be displayed. It would be used as a "hidden" buffer

Example :

1. Creating a "virtual" bitmap
2. Loading of a big size picture in this buffer
3. Paste image in the bitmap
4. Creating small size picture which are actually pieces of the big size one
5. Closing of the virtual bitmap

Your example should be enough for what he plans to do

He finally asks if your example could be used evn if the main context is initialized with MGLUT.

He thanks you a lot

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@AmiDARK

If you don't need doublebuffering the set the the value of MGLCC_PrivateBuffers to 1 and set the buffer using MGLCC_FrontBuffer only. (see minigl/gl.h for afraction more info

If you are going to use these functions alongside GLUT things could get alittle 'hacky' really they are designed to write a replacement for GLUT (they were specifically writen to implement Ghost, blenders window / GL management system, though I did try to make them general)

This assumes you have allready started GLUT

The current GLUT library interface is held in a global variable

struct GlutIFace * __glut_current_context;

to get the glutcontext from the interface use the GET_INSTANCE macro define in glut.h

GLUTcontext ctx = (GLUTcontext)GET_INSTANCE(__glut_current_context);

The minigl context used by glut can be found by doing

struct MiniGLIFace * glut_miniglcontext = ctx->__glutContext;


If say your custom context is amidarkspecial_miniglcontext then before you call any GL function that you want to operate on your speacial rgb buffer call:


mglMakeCurrent(amidark_special_miniglcontext);

then restore the glut context with


mglMakeCurrent(glut_miniglcontext);

You should probably ensure that you have called GLEnd() before swapping contexts like this. Maybe GLWait()

Your going to have to be particularly careful if you are multitasking.

This is abit nasty to be honest. I would be tempted abandon Glut, if you need to do much of this kind of stuff, but then ofcourse you will need to write your own event handlers etc so you may not like to do that.

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@translators

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@broadblues

Actually, my objective is to have a working environment.
So the faster is the best (even if it's not 100% the faster engine).
After, when Gallium 3D will be out and ready, I'll start a new version of the engine using Gallium3D ...

Thank you for these extra informations.

Kindest Regards,
AmiDARK

@AmiDARK

Hello AmiDark

Have a look to cow3d on aminet : it use Warp3d for drawing on a non visible bitmap
(then it copy the bitmap to the window)
This example dont use minigl but directly warp3d but certainly the idea stay the same

Alain Thellier

@BinoX

Quote:

Can you not just use glReadPixels after creating the image?

glReadPixels() is really slow function (as it requires GFX RAM => RAM transfers) and should be avoided, whenever possible. Of course it won't matter that much if done "only at initialization", but should definitely be avoided, if it's per frame, or even worse, multiple times per frame. Not sure which one this case is.

Also, this approach can downgrade 24bit images to 15/16bit, if the screenmode isn't 24/32bit (in case that matters)

@AmiDARK

Quote:

Sample : 1. Create virtual bitmap 2. Load a big image 3. Paste the image in the buffer 4. Create small images from the big images 5. Close the bitmap

One question, why are you doing this?

If you are f.ex. sprite sheets to single textures, why are you doing that? You can just use a single texture, and change texture coords accordingly. You can get the X & Y coordinates for same size sprites in sheet from single ID number with / and % operators nicely.

With this approach, you might also be able to reduce glBindTexture() calls, use of which should also be reduced, whenever possible.

Note: With sprite sheets, there can be blending issues at the borders of the image with blending in use.

Hi Jupp3,

AmiDARK Engine is a GDK ( Game Development Kit ) highly inspired from DarkBASIC Professional and DarkGDK ( from TheGameCreators : http://www.thegamecreators.com )

Their GDK contains functions to create and use *virtual non displayable bitmaps*
For Example : Create Bitmap bNumber, Width, Height
And we can draw inside these bitmaps.

I just need to reproduce these commands/functions
The sample was just to show on of the possible usage of virtuals bitmaps.

Kindest Regards,
AmiDARK