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Loading JPEG as Texture

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Hey I wanted to add JPEG support for a game Iam making, I was wondering if anyone knows of where I can find some good tutorials, or source on how to load JPEG as a texture to use with a OpenGL App. TY!

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yeah the thing is I would really really like to avoid adding any extra libaries right now, I would like to see some source on how to do it with a file stream or something and set it up as a texture.

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DevIL provides this function & easy integration into OpenGL. Plus it allows images of any size (not limited to power of 2) If you want to write your own then I'd suggest looking at existing loaders (like the bmp & tga ones on NeHe) for examples of how to go about writing a loader.

www.wotsit.org will help you in finding file format information. It's more straightforward than you think.

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Loading JPEG's is not easy, the compression is very complex and it is best that you just use a library for it. There are plenty out there and I just downloaded Nexgen IPL I had to find version 2.8 from somewhere else though since that site has dead links to the zip files. Just found that link again Directory where the some of the zips can be found, I recommend "btnexgenipl-2.8.3.zip"

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All you gotta do TempHolder is use NeHe's IPicture code. NO extra libraries, it just uses Windows files. It's very simple and well, is the best thing to use in this case IMO.

Just to make it easier for you, all you gotta do is this:
1. Copy the function into your code

int BuildTexture(char *szPathName, GLuint &texid) // Load Image And Convert To A Texture
HDC hdcTemp; // The DC To Hold Our Bitmap
HBITMAP hbmpTemp; // Holds The Bitmap Temporarily
IPicture *pPicture; // IPicture Interface
OLECHAR wszPath[MAX_PATH+1]; // Full Path To Picture (WCHAR)
char szPath[MAX_PATH+1]; // Full Path To Picture
long lWidth; // Width In Logical Units
long lHeight; // Height In Logical Units
long lWidthPixels; // Width In Pixels
long lHeightPixels; // Height In Pixels
GLint glMaxTexDim ; // Holds Maximum Texture Size

if (strstr(szPathName, "http://")) // If PathName Contains http:// Then...
strcpy(szPath, szPathName); // Append The PathName To szPath
else // Otherwise... We Are Loading From A File
GetCurrentDirectory(MAX_PATH, szPath); // Get Our Working Directory
strcat(szPath, "\\"); // Append "\" After The Working Directory
strcat(szPath, szPathName); // Append The PathName

MultiByteToWideChar(CP_ACP, 0, szPath, -1, wszPath, MAX_PATH); // Convert From ASCII To Unicode
HRESULT hr = OleLoadPicturePath(wszPath, 0, 0, 0, IID_IPicture, (void**)&pPicture);

if(FAILED(hr)) // If Loading Failed
return FALSE; // Return False

hdcTemp = CreateCompatibleDC(GetDC(0)); // Create The Windows Compatible Device Context
if(!hdcTemp) // Did Creation Fail?
pPicture->Release(); // Decrements IPicture Reference Count
return FALSE; // Return False (Failure)

glGetIntegerv(GL_MAX_TEXTURE_SIZE, &glMaxTexDim); // Get Maximum Texture Size Supported

pPicture->get_Width(&lWidth); // Get IPicture Width (Convert To Pixels)
lWidthPixels = MulDiv(lWidth, GetDeviceCaps(hdcTemp, LOGPIXELSX), 2540);
pPicture->get_Height(&lHeight); // Get IPicture Height (Convert To Pixels)
lHeightPixels = MulDiv(lHeight, GetDeviceCaps(hdcTemp, LOGPIXELSY), 2540);

// Resize Image To Closest Power Of Two
if (lWidthPixels <= glMaxTexDim) // Is Image Width Less Than Or Equal To Cards Limit
lWidthPixels = 1 << (int)floor((log((double)lWidthPixels)/log(2.0f)) + 0.5f);
else // Otherwise Set Width To "Max Power Of Two" That The Card Can Handle
lWidthPixels = glMaxTexDim;

if (lHeightPixels <= glMaxTexDim) // Is Image Height Greater Than Cards Limit
lHeightPixels = 1 << (int)floor((log((double)lHeightPixels)/log(2.0f)) + 0.5f);
else // Otherwise Set Height To "Max Power Of Two" That The Card Can Handle
lHeightPixels = glMaxTexDim;

// Create A Temporary Bitmap
BITMAPINFO bi = {0}; // The Type Of Bitmap We Request
DWORD *pBits = 0; // Pointer To The Bitmap Bits

bi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER); // Set Structure Size
bi.bmiHeader.biBitCount = 32; // 32 Bit
bi.bmiHeader.biWidth = lWidthPixels; // Power Of Two Width
bi.bmiHeader.biHeight = lHeightPixels; // Make Image Top Up (Positive Y-Axis)
bi.bmiHeader.biCompression = BI_RGB; // RGB Encoding
bi.bmiHeader.biPlanes = 1; // 1 Bitplane

// Creating A Bitmap This Way Allows Us To Specify Color Depth And Gives Us Imediate Access To The Bits
hbmpTemp = CreateDIBSection(hdcTemp, &bi, DIB_RGB_COLORS, (void**)&pBits, 0, 0);

if(!hbmpTemp) // Did Creation Fail?
DeleteDC(hdcTemp); // Delete The Device Context
pPicture->Release(); // Decrements IPicture Reference Count
return FALSE; // Return False (Failure)

SelectObject(hdcTemp, hbmpTemp); // Select Handle To Our Temp DC And Our Temp Bitmap Object

// Render The IPicture On To The Bitmap
pPicture->Render(hdcTemp, 0, 0, lWidthPixels, lHeightPixels, 0, lHeight, lWidth, -lHeight, 0);

// Convert From BGR To RGB Format And Add An Alpha Value Of 255
for(long i = 0; i < lWidthPixels * lHeightPixels; i++) // Loop Through All Of The Pixels
BYTE* pPixel = (BYTE*)(&pBits); // Grab The Current Pixel
BYTE temp = pPixel[0]; // Store 1st Color In Temp Variable (Blue)
pPixel[0] = pPixel[2]; // Move Red Value To Correct Position (1st)
pPixel[2] = temp; // Move Temp Value To Correct Blue Position (3rd)

// This Will Make Any Black Pixels, Completely Transparent (You Can Hardcode The Value If You Wish)
if ((pPixel[0]==0) && (pPixel[1]==0) && (pPixel[2]==0)) // Is Pixel Completely Black
pPixel[3] = 0; // Set The Alpha Value To 0
else // Otherwise
pPixel[3] = 255; // Set The Alpha Value To 255

glGenTextures(1, &texid); // Create The Texture

// Typical Texture Generation Using Data From The Bitmap
glBindTexture(GL_TEXTURE_2D, texid); // Bind To The Texture ID
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); // (Modify This For The Type Of Filtering You Want)
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR); // (Modify This For The Type Of Filtering You Want)
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, lWidthPixels, lHeightPixels, 0, GL_RGBA, GL_UNSIGNED_BYTE, pBits); // (Modify This If You Want Mipmaps)

DeleteObject(hbmpTemp); // Delete The Object
DeleteDC(hdcTemp); // Delete The Device Context

pPicture->Release(); // Decrements IPicture Reference Count

return TRUE; // Return True (All Good)

2. Add in the header files needed:

#include <windows.h> // Header File For Windows
#include <olectl.h> // Header File For The OLE Controls Library
#include <math.h> // Header File For The Math Library

3. Now to use it, change it so it matches your file and texture:

// Load .JPG From A File (1st Texture)
if (!BuildTexture("Data/NeHe.jpg", texture))
return FALSE; // Return False If Loading Failed

Then that's it! You can even load from the web as seen in the example.

[Edited by - Drew_Benton on October 9, 2005 3:44:43 AM]

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