Understanding of OpenGL

Understanding of OpenGL Texture Mapping TA: Dong Hyun JeongInstructor : Dr. Kalpathi Subramanian

Purpose • How to upload textures in OpenGL • Understanding of several existing techniques and GPU-based texture mapping

Upload textures • Define a texture • glBindTexture • glPixelStorei • glTexParameteri • glTexEnvf • glTexImage2D • Calling the defined texture • glBindTexture Without Mipmap With Mipmap

Binding and setting • glBindTexture(GL_TEXTURE_2D, ID); • Texture "id" is just a number that we use it for calling the texture. • glPixelStorei(GL_UNPACK_ALIGNMENT, 1); • Defining how the data that is going to be uploaded is aligned. • glTexParameteri • Wrap Mode • glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT); • glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT); • . Wrap S : GL_CLAMP Wrap T : GL_CLAMP Wrap S : GL_CLAMP Wrap T : GL_CLAMP Wrap S : GL_CLAMP Wrap T : GL_CLAMP Wrap S : GL_CLAMP Wrap T : GL_CLAMP

Binding and setting II • glTexParameteri • Scale Mode • Magnification is when each texel is larger than each pixel. • Minification is when each texel is smaller than each pixel. • glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); • glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); • . Min / Max Filter : GL_NEAREST Min / Max Filter : GL_LINEAR

Environment settings • glTexEnvf • Set the environment variables for the current texture. • glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE); • glTexImage2D • Upload the texture to the video memory where it will be ready for us to use in our programs • glTexImage2D (GL_TEXTURE_2D, 0, GL_RGB, imageWidth, imageHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, imageData); • . GL_RGB GL_RGB4

Specifying a Texture • Texture is specified as an array of texels: • GLubyte imageData1[3 * 256 * 256]when GL_RGB is set. Height is power of 2 One byte for each of red, green and blue. Width is power of 2

Simple example glBindTexture (GL_TEXTURE_2D, id); glPixelStorei (GL_UNPACK_ALIGNMENT, 1); glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT); glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT); glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexEnvf (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE); glTexImage2D (GL_TEXTURE_2D, 0, m_texFormat, imageWidth, imageHeight, 0, m_texFormat, GL_UNSIGNED_BYTE, imageData); glBindTexture (GL_TEXTURE_2D, id); glBegin (GL_QUADS); glTexCoord2f (0.0, 0.0); glVertex3f (0.0, 0.0, 0.0); glTexCoord2f (1.0, 0.0); glVertex3f (10.0, 0.0, 0.0); glTexCoord2f (1.0, 1.0); glVertex3f (10.0, 10.0, 0.0); glTexCoord2f (0.0, 1.0); glVertex3f (0.0, 10.0, 0.0); glEnd ();

Texture Drawing (0,1) (1,1) (0,0) (1,0) (1,0) (0,0) (1,1) (0,1) (1,0) (1,1) (0,0) (0,1) Order : (0,0) > (1,0) > (1,1) > (0,1)

Bump mapping • Evaluate the lighting equation per pixel Pixel Map Bump Map http://www.paulsprojects.net/tutorials/simplebump/simplebump.html

Shadow Mapping • One of many different ways of producing shadows in graphics applications • No knowledge or processing of the scene geometry is required, since shadow mapping is an image space technique, working automatically with objects created or altered on the GPU. • Only a single texture is required to hold shadowing information for each light; the stencil buffer is not used. • Avoids the high fill requirement of shadow volumes. • Method • Create shadow mapping as a depth test • http://www.paulsprojects.net/tutorials/smt/smt.html

Alpha Mapping • Use RGBA color channels • glTexImage2D(GL_TEXTURE_2D, 0, 4, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, image);

Light Mapping • Contains luminance information • Calculate the lightmap's UV coordinates • Project the polygon's coordinates onto a primary axis plane • Convert the new coordinates to 2D texture space • http://www.flipcode.com/articles/article_lightmapping.shtml • http://www.alsprogrammingresource.com/lightmapping.html • http://www.daionet.gr.jp/~masa/rthdribl/index.html

Gloss Mapping • Modify the specular highlight • Scale the specular value by the gloss map value + + Before After

Environmental Mapping • Set The Texture Generation Mode For S and T To Sphere Mapping • glTexGeni(GL_S, GL_TEXTURE_GEN_MODE, GL_SPHERE_MAP); glEnable(GL_TEXTURE_GEN_S); glEnable(GL_TEXTURE_GEN_T); glBindTexture(GL_TEXTURE_2D, texture[filter+(filter+1)]); // Shere Map glPushMatrix(); glRotatef(xrot,1.0f,0.0f,0.0f); glRotatef(yrot,0.0f,1.0f,0.0f); glDrawCube(); glPopMatrix(); glDisable(GL_TEXTURE_GEN_S); glDisable(GL_TEXTURE_GEN_T); glBindTexture(GL_TEXTURE_2D, texture[filter*2]); // Environmental Map glPushMatrix(); glTranslatef(0.0f, 0.0f, -24.0f); -Draw Background Object glPopMatrix(); glBindTexture(GL_TEXTURE_2D, texture[filter+(filter+1)]); http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=23

Procedural Techniques I • Use of code segments or algorithms to generate object description, attribute, motion, etc. • Simple Noise • Perlin Noise • Cellular Texturing(Voronoi Diagram) • Reaction-Diffusion(Partial Differential)

Procedural Techniques II Sample_Procedure(x,y,color) { static int first=1; color.r=color.g=color.b=0; if(first) { first=0; for (i=0; i < 20; i++) { center[i].x = drand48()*10; center[i].y = drand48()*10; radius[i] = drand48*.5; radius[i] *=radius[i]; color[i].r = drand48(); color[i].g=drand48(); color[i].b=drand48(); } } for (i=0; i < 20; i++) { dist_sq = (center[i].x-x)*(center[i].x-x) + (center[i].y-y)*(center[i].y-y) if (dist_sq < radius[i]) color=color[i]; break; } } http://www.csee.umbc.edu/~ebert/691/Au00/Notes/procedural.html

Using Texture coordinates • Loading models • Importing Wavefront OBJ file to display • *.obj file includes vertex, texture coordinate, and face numbers Rendered using 3DS MAX without texture Rendered using 3DS MAX with texture

Q & A

Understanding of OpenGL