CS 4363/6353 TEXTURE MAPPING PART II

WHAT WE KNOW We can open image files for reading We can load them into texture buffers We can link that texture buffer to a variable in the fragment shader We can access the texture in the fragment shader using a sampler2D

RECTANGLE TEXTURES There’s another mode called GL_TEXTURE_RECTANGLE Works just like GL_TEXTURE_2D, but… Texture coordinate range is the width and height of the image (not normalized) Can’t be mipmapped Texture coordinates cannot repeat Do not support compression Useful for when you need to process image data (image processing), not just texture Typically, you create an orthographic projection with 0,0 on the bottom left First quadrant of the Cartesian system

OpenGL SuperBible Example

CUBE MAPPING Used for “skyboxes” Used for faking reflections Comprised of 6 individual images Treated as one texture Can be mipmapped ( glGenerateMipmap (GL_TEXTURE_CUBE_MAP) ) We’re going to have 3 texture coordinates! S T R It’s easiest to think of this as a normal because the cube “surrounds” you

Neg X Neg Y Neg Z Pos X Pos Y Pos Z OpenGL SuperBible – Chapter 7

LOADING CUBE MAPS Create/Bind a buffer like normal Still load using glTexImage2D, but must pass: GL_TEXTURE_CUBE_MAP_POSITIVE_X GL_TEXTURE_CUBE_MAP_NEGATIVE_X GL_TEXTURE_CUBE_MAP_POSITIVE_Y GL_TEXTURE_CUBE_MAP_NEGATIVE_Y GL_TEXTURE_CUBE_MAP_POSITIVE_Z GL_TEXTURE_CUBE_MAP_NEGATIVE_Y Example: glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X, 0, GL_RGBA, w, h, 0, GL_BGR, GL_UNSIGNED_BYTE, bitmap_data);

TEXTURE PARAMETERS Still have MAG and MIN filters, but… Specify it’s a GL_TEXTURE_CUBE_MAP Specify how to wrap each texture coordinate Example glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);

SKYBOXES Literally just a giant box with a texture on it It follows the camera! It doesn’t rotate with the camera How do we map the cube map to the cube? What are the texture coordinates?

SKYBOXES Literally just a giant box with a texture on it It follows the camera! It doesn’t rotate with the camera How do we map the cube map to the cube? What are the texture coordinates? The same as their positions!

SKYBOXES Literally just a giant box with a texture on it It follows the camera! It doesn’t rotate with the camera How do we map the cube map to the cube? What are the texture coordinates? How do we sample the texture in our fragment shader? Using a sampleCube variable

// Skybox Shader by Richard S. Wright, Jr. #version 330 in vec4 vVertex; uniform mat4 mvpMatrix; varying vec3 vVaryingTexCoord; void main (void) { vVaryingTexCoord = normalize (vVertex.xyz); gl_Position = mvpMatrix * vVertex; } #version 330 out vec4 vFragColor; uniform samplerCube cubeMap; varying vec3 vVaryingTexCoord; void main (void) { vFragColor = texture (cubeMap, vVaryingTexCoord); }

REFLECTIONS OpenGL SuperBible – Chapter 7

// Reflection Shader – Richard S. Wright Jr. #version 330 in vec4 vVertex; in vec3 normal; uniform mat4 mvpMatrix; uniform mat4 mvMatrix; uniform mat3 normalMatrix; // Just the rots of the mv uniform mat4 mInverseCamera;// The camera matrix inverted smooth out vec3 vVaryingTexCoord; void main (void) { // Normal in eye space – only rots vec3 vEyeNormal = normalMatrix * vNormal; // Vertex in eye space vec4 vVert4 = mvMatrix * vVertex; vec3 vEyeVertex = normalize(vVert4.xyz/vVert4.w); // Calculate a reflection vector, then invert it vec4 vCoords = vec4(reflect(vEyeVertex, vEyeNormal), 1.0); vCoords = mInverseCamera * vCoords; vVaryingTexCoord.xyz = normalize(vCoords.xyz); gl_Position = mvpMatrix * vVertex; }

USING MULTIPLE TEXTURES Second texture useful for: Adding multiple colors together Using it as a bump map Using it as a specular map Using it as a transparency map

FOR COLOR ALONE

BUMP MAPPING Used to approximate very rough surfaces Using the second texture to adjust the normals of the surface Per fragment, not per vertex In the case below, all N◦L is the same

BUMP MAPPING Used to approximate very rough surfaces Using the second texture to adjust the normals of the surface Per fragment, not per vertex In the case below, all N◦L is not the same Gives off a different amount of light! Note – the geometry has not changed!

EXAMPLE

EXAMPLE FROM BOOK

AN EXTREME EXAMPLE

PARALLAX MAPPING Approximate parallax Changes the texture coordinate based on view vector and normal Need a height map

BILLBOARDING Image always faces the camera (think of the math!) Typically has transparency Useful for trees Useful for particle effects

POINT SPRITES OpenGL 1.5 Based on billboarding Can place a 2D texture using a single point! Previously, needed two triangles 1/4 th the bandwidth No aligning the quad to face the camera Using them Bind a 2D texture Draw using glPolygonMode (GL_FRONT, GL_POINTS)

TEXTURE ARRAYS Packing several images into a single texture units (GL_TEXTURE0) Good for 2D animations Similar use: glBindTexture (GL_TEXTURE_2D_ARRAY, texBufID); glTexParameteri (GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MIN_FILTER, GL_LINEAR); However, to load the image, we are now in 3D! glTexImage3D (GL_TEXTURE_2D_ARRAY, level, internal_format, w, h, depth, border, format, NULL); The depth parameter specifies how many images are in the array

LOADING THE ARRAYS for (int i = 0; i < num_images; i++) { data = loadBitmap (“image”+i+”.bmp”); glTexSubImage(GL_TEXTURE_2D_ARRAY, 0, 0, 0, i, w, h, 1, GL_BGR, GL_UNSIGNED_BYTE, data); }

ACCESSING THE IMAGES Normally, you specify the image index from the client side GLuint loc = glGetUniform (progID, “image_num”); glUniform1f (loc, counter); // some int Then, in the vertex shader, use it as the 3 rd texture coordinate: uniform float image_num; in vec4 vTexCoords; smooth out vec3 imageTexCoords; void main (void) { imageTexCoords.st = vTexCoords.st; imageTexCoords.p = image_num; … }

YOUR FRAGMENT SHADER Must have a sampler2DArray variable Must use the texture2DArray function uniform sampler2DArray texture; smooth in vec3 imageTexCoords; out vFragColor; void main () { vFragColor = texture2DArray (texture, imageTexCoods.stp); }