Jeff Molofee - NeHe's OpenGL Tutorials

Before we start… The "red book" defines a Sphere map as a picture of the scene on a metal ball from infinite distance away and infinite focal point. Well that is impossible to do in real life. The best way I have found to create a good sphere map image without using a Fish eye lens is to use Adobe's Photoshop program.

Creating a Sphere Map In Photoshop:

First you will need a picture of the environment you want to map onto the sphere. Open the picture in Adobe Photoshop and select the entire image. Copy the image and create a new PSD (Photoshop Format) the new image should be the same size as the image we just copied. Paste a copy of the image into the new window we've created. The reason we make a copy is so Photoshop can apply its filters. Instead of copying the image you can select mode from the drop down menu and choose RGB mode. All of the filters should then be available.

Next we need to resize the image so that the image dimensions are a power of 2. Remember that in order to use an image as a texture the image needs to be 128×128, 256×256, etc. Under the image menu, select image size, uncheck the constraint proportions checkbox, and resize the image to a valid texture size. If your image is 100×90, it's better to make the image 128×128 than 64×64. Making the image smaller will lose alot of detail.

The last thing we do is select the filter menu, select distort and apply a spherize modifier. You should see that the center of the picture is blown up like a balloon, now in normal sphere maps the outer area will be blackened out, but it doesn't really matter. Save a copy of the image as a .BMP and you're ready to code!

We don't add any new global variables this time but we do modify the texture array to hold 6 textures.

GLuint texture[6]; // Storage For 6 Textures

The next thing I did was modify the LoadGLTextures() function so we can load in 2 bitmaps and create 3 filters. (Like we did in the original texturing tutorials). Basically we loop through twice and create 3 textures each time using a different filtering mode. Almost all of this code is new or modified.

int LoadGLTextures() // Load Bitmaps And Convert To Textures

{

int Status=FALSE; // Status Indicator

AUX_RGBImageRec *TextureImage[2]; // Create Storage Space For The Texture

memset(TextureImage,0,sizeof(void *)*2); // Set The Pointer To NULL

// Load The Bitmap, Check For Errors, If Bitmap's Not Found Quit

if ((TextureImage[0]=LoadBMP("Data/BG.bmp")) && // Background Texture

(TextureImage[1]=LoadBMP("Data/Reflect.bmp"))) // Reflection Texture (Spheremap)

{

Status=TRUE; // Set The Status To TRUE

glGenTextures(6, &texture[0]); // Create Three Textures

for (int loop=0; loop<=1; loop++) {

// Create Nearest Filtered Texture

glBindTexture(GL_TEXTURE_2D, texture[loop]); // Gen Tex 0 And 1

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

glTexImage2D(GL_TEXTURE_2D, 0, 3, TextureImage[loop]->sizeX, TextureImage[loop]->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, TextureImage[loop]->data);

// Create Linear Filtered Texture

glBindTexture(GL_TEXTURE_2D, texture[loop+2]); // Gen Tex 2, 3 And 4

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

glTexImage2D(GL_TEXTURE_2D, 0, 3, TextureImage[loop]->sizeX, TextureImage[loop]->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, TextureImage[loop]->data);

// Create MipMapped Texture

glBindTexture(GL_TEXTURE_2D, texture[loop+4]); // Gen Tex 4 and 5

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);

gluBuild2DMipmaps(GL_TEXTURE_2D, 3, TextureImage[loop]->sizeX, TextureImage[loop]->sizeY, GL_RGB, GL_UNSIGNED_BYTE, TextureImage[loop]->data);

}

for (loop=0; loop<=1; loop++) {

if (TextureImage[loop]) // If Texture Exists

{

if (TextureImage[loop]->data) // If Texture Image Exists

{

free(TextureImage[loop]->data); // Free The Texture Image Memory

}

free(TextureImage[loop]); // Free The Image Structure

}

}

}

return Status; // Return The Status

}

We'll modify the cube drawing code a little. Instead of using 1.0 and –1.0 for the normal values, we'll use 0.5 and –0.5. By changing the value of the normal, you can zoom the reflection map in and out. If the normal value is high, the image being reflected will be bigger, and may appear blocky. By reducing the normal value to 0.5 and –0.5 the reflected image is zoomed out a bit so that the image reflecting off the cube isn't all blocky looking. Setting the normal value too low will create undesirable results.

GLvoid glDrawCube() {

glBegin(GL_QUADS);

// Front Face

glNormal3f( 0.0f, 0.0f, 0.5f);

glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, –1.0f, 1.0f);

glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, –1.0f, 1.0f);

glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, 1.0f, 1.0f);

glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, 1.0f);

// Back Face

glNormal3f( 0.0f, 0.0f,-0.5f);

glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, –1.0f, –1.0f);

glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, 1.0f, –1.0f);

glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, 1.0f, –1.0f);

glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, –1.0f, –1.0f);

// Top Face

glNormal3f( 0.0f, 0.5f, 0.0f);

glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, –1.0f);

glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, 1.0f, 1.0f);

glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, 1.0f, 1.0f);

glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, 1.0f, –1.0f);

// Bottom Face

glNormal3f( 0.0f,-0.5f, 0.0f);

glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, –1.0f, –1.0f);

glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, –1.0f, –1.0f);

glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, –1.0f, 1.0f);

glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, –1.0f, 1.0f);

// Right Face

glNormal3f( 0.5f, 0.0f, 0.0f);

glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, –1.0f, –1.0f);

glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, 1.0f, –1.0f);

glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, 1.0f, 1.0f);

glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, –1.0f, 1.0f);

// Left Face

glNormal3f(-0.5f, 0.0f, 0.0f);

glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, –1.0f, –1.0f);

glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, –1.0f, 1.0f);

glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, 1.0f, 1.0f);

glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, –1.0f);