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# OpenGL Trouble loading and displaying with transparency, 8bit indexed bitmaps

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I am working on a project, that uses some legacy graphics, that are in an 8bit indexed bitmaps.  These are the ones with a 1 byte pixel, pointing to an array of 256 colors.

So far, this is how I have been doing things.... (note, I'm using C#, with OpenTK, although a solution in C++ can be easily converted)

Bitmap bitmap = new Bitmap(path);
System.Drawing.Imaging.BitmapData textureData = bitmap.LockBits(
new Rectangle(0, 0, bitmap.Width, bitmap.Height),
System.Drawing.Imaging.ImageLockMode.ReadOnly,
System.Drawing.Imaging.PixelFormat.Format8bppIndexed);

int srcmax = textureData.Height * textureData.Stride;
byte[] origBytes = new Byte[srcmax];
Marshal.Copy(textureData.Scan0, origBytes, 0, srcmax);

bitmap.UnlockBits(textureData);


this gives me the bitmap pixel data (the 1 byte index numbers) in textureData.

So now, I very slowly and very painfully, go through the data, as such....

                        //loop through all the pixels
byte[] data = new byte[(bitmap.Width * bitmap.Height) * 4];

int srcloc = 0;
int dstloc = 0;
byte index;
Color color;
for (int y = 0; y < textureData.Height; y++)
{
srcloc = y * textureData.Stride;
for (int x = 0; x < textureData.Width; x++)
{
index = origBytes[srcloc];
if (index == 0)
{
data[dstloc] = 0;
data[dstloc + 1] = 0;
data[dstloc + 2] = 0;
data[dstloc + 3] = 0;
}
else
{
color = bitmap.Palette.Entries[index];
data[dstloc] = color.R;
data[dstloc + 1] = color.G;
data[dstloc + 2] = color.B;
data[dstloc + 3] = color.A;
}
dstloc += 4;
srcloc++;
}
}


as you can see, I am looking at the color, pointed to, by each pixel index... and manually reversing the red, and blue values, and also, setting alpha to 0, when the index number is 0.  This converted data is then used to create an opengl texture, as follows...

                GL.Enable(EnableCap.Texture2D);
uint textureID = 0;
GL.GenTextures(1, out textureID);

GL.BindTexture(TextureTarget.Texture2D, ret.ID);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureWrapS, (float)TextureWrapMode.Clamp);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureWrapT, (float)TextureWrapMode.Clamp);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMinFilter, (float)TextureMinFilter.Nearest);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMagFilter, (float)TextureMagFilter.Nearest);
GL.TexImage2D(TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba, width, height, 0,
PixelFormat.Rgba, PixelType.UnsignedByte, pixelData);

GL.Disable(EnableCap.Texture2D);



Now... this totally works, I end up with a rgba opengl texture2d, with transparency that can be used to texture a quad  and it looks perfect.... only problem is the super slow speed of going through each pixel, as some of these images are > 800x800

So... If anyone knows of a better solution, something faster, or if you know of anything I seem to be doing wrong (opengl wise, as I am an opengl noob) please let me know.

Thanks

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Are you sure it is "super slow"? However, some thoughts:

1.) One thing is to avoid the in-loop case distinction. If Palette.Entries[0] would store {0,0,0,0} then index ==0 would be handled as any other index, and the if-clause could be eliminated.

2.) Another thing is perhaps the possibility to reduce the 4x1-byte writes to 1x4-bytes write, but I'm not sure; perhaps modern hardware / compilers can hide that anyway. Maybe somebody else can comment on this attempt ...

3.) If this step is in time critical code, then move it out into a pre-processing step if possible.

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Thanks so much for your input.

Well, the case with Palette.Entries[0], is that it's alpha value is non 0, and I really don't care what color the pixels are for index 0, as long as it is transparent.  I cant edit the original images, unless there is some magical opengl, trick to mass convert data or something, I'm afraid I'll have to check and set to alpha 0 each time I hit an index 0 byte.

I see what you mean, as far as writing 1x4 bytes, not sure if this would be a speed increase, but its something I will try, just to see if I get different results.

It is a time critical piece of code, and I do have it in a 'title/loading' screen, its just.... slow loading.

Now you mention, am I sure its 'super slow'... yeah, it kinda is... and actually that is a bit surprising, even for an 800x800 image... I would think it would be faster on a modern computer.  So, I'm wondering if the part that is taking up so much time, might be the part of the code where I am reading in the Bitmap, with LockBits, and copying its data.

I plan to keep trying and experimenting

If anyone has any other input or have used 8bit indexed bitmaps.... please share some secrets, thanks.

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It is definately the 'looping' through the indexes that is causing the slow operation.

I have been searching and searching online for a solution, and came across something interesting...

I've seen

GL.TexImage2D(TextureTarget.Texture2D, 0,
PixelInternalFormat.Rgba,
bitmap.Width, bitmap.Height, 0,
PixelFormat.ColorIndex, PixelType.UnsignedByte, data);


now, the PixelFormat is ColorIndex.... this is what I need... however, when I use this, I get pure black images, no transparency...

So, I think I must be missing the 'color palette' somewhere... I'm trying to discover, how to let opengl know the data of the colorpalette tha the ColorIndex will look at.

I also read this...

"Similarly, to offset the color indices of a bitmap to the palette entries you have defined for it, use

glPixelTransferi(GL_INDEX_OFFSET, bitmap_entry);"

it says 'the palette entries you have defined', and im assuming this is 'bitmap_entry', but nothing shows 'HOW' to define the palette entries

So... I'm feeling more lost than ever, surely surely someone has used indexed graphics, and knows how to do this, but the lack of information on the web is troubling, i'm thinking, is it even possible anymore?

Thanks for any help

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I think this line makes your code slow:

color = bitmap.Palette.Entries[index];


Because this says: "This property returns a copy of the ColorPalette object used by this Image."

Maybe just grab the palette/entries first so you can access them directly?

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Well, the case with Palette.Entries[0], is that it's alpha value is non 0, and I really don't care what color the pixels are for index 0, as long as it is transparent.  I cant edit the original images, unless there is some magical opengl, trick to mass convert data or something, I'm afraid I'll have to check and set to alpha 0 each time I hit an index 0 byte.

Make a copy of the palette in an own byte array and set the entry at index 0 accordingly. That has nothing to do with OpenGL.

now, the PixelFormat is ColorIndex.... this is what I need... however, when I use this, I get pure black images, no transparency...
So, I think I must be missing the 'color palette' somewhere... I'm trying to discover, how to let opengl know the data of the colorpalette tha the ColorIndex will look at.

Color index mode has been deprecated in 2009 with OpenGL 3.0. You should not use it any more.

Because this says: "This property returns a copy of the ColorPalette object used by this Image."

Oh yes, a single access would be better then.

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Its too bad there is no apparent 'native support' for 8bit images in opengl anymore.  However, I did not know it was getting a copy of the entire palette on each call, I tried to suggestion of making one copy to an array, and using the array, and the results were 100% faster.

I cant even tell how long its taking to load, as it zips through the files.

Thanks so much.

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I literally can't find what is wrong. If you need more code, ask me to post it. I will also attach all the source files.
Brain.cpp
Error.cpp
IndexBuffer.cpp
Input.cpp
Renderer.cpp
Scene.cpp
Shader.cpp
Sprite.cpp
Texture.cpp
VertexArray.cpp
VertexBuffer.cpp
VertexBufferLayout.cpp
Window.cpp
Brain.h
Error.h
IndexBuffer.h
Input.h
Renderer.h
Scene.h
Shader.h
SpaceShooterEngine.h
Sprite.h
Texture.h
VertexArray.h
VertexBuffer.h
VertexBufferLayout.h
Window.h

• Hello fellow programmers,
For a couple of days now i've decided to build my own planet renderer just to see how floating point precision issues
can be tackled. As you probably imagine, i've quickly faced FPP issues when trying to render absurdly large planets.

I have used the classical quadtree LOD approach;
I've generated my grids with 33 vertices, (x: -1 to 1, y: -1 to 1, z = 0).
Each grid is managed by a TerrainNode class that, depending on the side it represents (top, bottom, left right, front, back),
creates a special rotation-translation matrix that moves and rotates the grid away from the origin so that when i finally
normalize all the vertices on my vertex shader i can get a perfect sphere.
T = glm::translate(glm::dmat4(1.0), glm::dvec3(0.0, 0.0, 1.0)); R = glm::rotate(glm::dmat4(1.0), glm::radians(180.0), glm::dvec3(1.0, 0.0, 0.0)); sides[0] = new TerrainNode(1.0, radius, T * R, glm::dvec2(0.0, 0.0), new TerrainTile(1.0, SIDE_FRONT)); T = glm::translate(glm::dmat4(1.0), glm::dvec3(0.0, 0.0, -1.0)); R = glm::rotate(glm::dmat4(1.0), glm::radians(0.0), glm::dvec3(1.0, 0.0, 0.0)); sides[1] = new TerrainNode(1.0, radius, R * T, glm::dvec2(0.0, 0.0), new TerrainTile(1.0, SIDE_BACK)); // So on and so forth for the rest of the sides As you can see, for the front side grid, i rotate it 180 degrees to make it face the camera and push it towards the eye;
the back side is handled almost the same way only that i don't need to rotate it but simply push it away from the eye.
The same technique is applied for the rest of the faces (obviously, with the proper rotations / translations).
The matrix that result from the multiplication of R and T (in that particular order) is send to my vertex shader as r_Grid'.
// spherify vec3 V = normalize((r_Grid * vec4(r_Vertex, 1.0)).xyz); gl_Position = r_ModelViewProjection * vec4(V, 1.0); The r_ModelViewProjection' matrix is generated on the CPU in this manner.
// No the most efficient way, but it works. glm::dmat4 Camera::getMatrix() { // Create the view matrix // Roll, Yaw and Pitch are all quaternions. glm::dmat4 View = glm::toMat4(Roll) * glm::toMat4(Pitch) * glm::toMat4(Yaw); // The model matrix is generated by translating in the oposite direction of the camera. glm::dmat4 Model = glm::translate(glm::dmat4(1.0), -Position); // Projection = glm::perspective(fovY, aspect, zNear, zFar); // zNear = 0.1, zFar = 1.0995116e12 return Projection * View * Model; } I managed to get rid of z-fighting by using a technique called Logarithmic Depth Buffer described in this article; it works amazingly well, no z-fighting at all, at least not visible.
Each frame i'm rendering each node by sending the generated matrices this way.
// set the r_ModelViewProjection uniform // Sneak in the mRadiusMatrix which is a matrix that contains the radius of my planet. Shader::setUniform(0, Camera::getInstance()->getMatrix() * mRadiusMatrix); // set the r_Grid matrix uniform i created earlier. Shader::setUniform(1, r_Grid); grid->render(); My planet's radius is around 6400000.0 units, absurdly large, but that's what i really want to achieve;
Everything works well, the node's split and merge as you'd expect, however whenever i get close to the surface
of the planet the rounding errors start to kick in giving me that lovely stairs effect.
I've read that if i could render each grid relative to the camera i could get better precision on the surface, effectively
getting rid of those rounding errors.

My question is how can i achieve this relative to camera rendering in my scenario here?
I know that i have to do most of the work on the CPU with double, and that's exactly what i'm doing.
I only use double on the CPU side where i also do most of the matrix multiplications.
As you can see from my vertex shader i only do the usual r_ModelViewProjection * (some vertex coords).

Thank you for your suggestions!

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