hallym university gve lab. 1 graphics and virtual environment laboratory 8 color and shading...

Hallym University GVE LAB.Hallym University GVE LAB.

1 Graphics and Virtual Environment LaboratoryGraphics and Virtual Environment Laboratory

88COLOR AND SHADINGCOLOR AND SHADING

PalettesPalettes 를 중심으로 를 중심으로



Windows PalettesWindows Palettes

The TRIANGLE and CCUBE example program work reasonably

well regardless of how many colors are available.

그러나 더 높은 depth color 를 사용하는 경우 훨씬 매끄러운

이미지를 만들어 낸다 .

예 ) 그림 8-12a (16 색 ) 와 그림 8-12b(1,600 만개색 )



Windows PalettesWindows PalettesColor Matching

Windows passes the 24-bit color value to the display driver which

converts the color to a 15- or 16-bit color value before dispalying it.



Windows PalettesWindows Palettes

Dithering

Color Approximation (dithering) : 4 bit color modes 의 경우 When you specify a color to use for drawing operations using glColor3ub,

- The nearest color of the 16 available to fulfill the request.

- For filling operation, dithering is used.



Windows PalettesWindows PalettesDithering :

A means of placing different colors close together to produce the

illusion of another composite color.

Ex) If you place yellow and blue squares together in a checkboard

pattern, the pattern will take on a greenish appearance.

glEnable(GL_DITHER)

DITHER.EXE

8 비트 이상 모드에서는 효과가 거의 없다 .



Windows PalettesWindows Palettes2 가지 경우 :

• Colors are evenly distributed across RGB color space

• Colors are selected to produce smooth shading of a surface

• 바다 , the image of a pipe’s cross section

• Near photographic quality

Palette Arbitration

CreatePalette() : create palette

hPalette : a handle of type HPALETTE



Windows PalettesWindows PalettesSystem Palette vs Private Palette( 해당 프로그램에서 사용하는 팔레트 ):

All applications must share the same system palette.

WM_QUERYNEWPALETTE :

- When application receives keyboard or mouse input focus.

WM_PALETTECHANGED : This message is sent to window that can

realize their palette but may not have the current focus.

RealizePalette() :

Application copies the palette entries from the private palette to

the system palette.

팔레트를 Realize 한다는 것은 프로그램이 private palette 를 system palette 로

복사하는 것을 의미한다 .



Windows PalettesWindows Palettes// Windows is telling the application that it may modify// the system palette. This message in essance asks the // application for a new palette.

case WM_QUERYNEWPALETTE:// If the palette was created.if(hPalette)

{int nRet;// Selects the palette into the current device contextSelectPalette(hDC, hPalette, FALSE);// Map entries from the currently selected palette to// the system palette. The return value is the number // of palette entries modified.nRet = RealizePalette(hDC);// Repaint, forces remap of palette in current windowInvalidateRect(hWnd,NULL,FALSE);return nRet;}

break;



Windows PalettesWindows Palettes // This window may set the palette, even though it is not the // currently active window. case WM_PALETTECHANGED:

// Don't do anything if the palette does not exist, or if// this is the window that changed the palette.if((hPalette != NULL) && ((HWND)wParam != hWnd))

{// Select the palette into the device contextSelectPalette(hDC,hPalette,FALSE);

// Map entries to system paletteRealizePalette(hDC);

// Remap the current colors to the newly realized paletteUpdateColors(hDC);return 0;}

break;

Contains the current window handle

receiving message



Creating PalettesCreating Palettes

case WM_CREATE:// Store the device contexthDC = GetDC(hWnd);

// Select the pixel formatSetDCPixelFormat(hDC); // 팔레트 만들기hPalette = GetOpenGLPalette(hDC);

// Create the rendering context and make it currenthRC = wglCreateContext(hDC);wglMakeCurrent(hDC, hRC);

break;

Do You Need a Palette?



Creating PalettesCreating Palettes HPALETTE GetOpenGLPalette(HDC hDC)

{HPALETTE hRetPal = NULL; // Handle to palette to be createdPIXELFORMATDESCRIPTOR pfd; // Pixel Format DescriptorLOGPALETTE *pPal; // Pointer to memory for logical paletteint nPixelFormat; // Pixel format indexint nColors; // Number of entries in paletteint i; // Counting variableBYTE RedRange,GreenRange,BlueRange; // Range for each color entry (7,7,and 3)

// Get the pixel format index and retrieve the pixel format descriptionnPixelFormat = GetPixelFormat(hDC);DescribePixelFormat(hDC, nPixelFormat, sizeof(PIXELFORMATDESCRIPTOR), &pfd);

// Does this pixel format require a palette? If not, do not create a// palette and just return NULLif(!(pfd.dwFlags & PFD_NEED_PALETTE))

return NULL;



The Palette’s StructureThe Palette’s Structure

typedef struct tagLOGPALETTE { WORD palVersion; WORD palNumEntries; PALETTEENTRY palPalEntry[1]; } LOGPALETTE;

LOGPALETTE *pPal;…..

pPal = (LOGPALETTE*)malloc(sizeof(LOGPALETTE) + ncolors * sizeof(PALETTEENTRY));



The 3-3-2 PaletteThe 3-3-2 Palette

7 6 5 4 3 2 1 0 8-bit Palette Index

Blueintensity

Greenintensity

Redintensity

Function to Create a palette for OpenGL Device context



The 3-3-2 PalettesThe 3-3-2 Palettes

PaletteEntry

Binary(B G R)

Blue Comp GreenComp

RedComp

0 00 000 000 0 0 01 00 000 001 0 0 1*255/7

2 00 000 010 0 0 2*255/7

3 00 000 011 0 0 3*255/7

9 00 001 001 0 1*255/7 1*255/7

10 00 001 010 0 1*255/7 2*255/7

137 10 001 001 2*255/3 1*255/7 1*255/7

138 10 001 010 2*255/3 1*255/7 2*255/7

255 11 111 111 3*255/3 7*255/7 7*255/7



Building the Palettes (Building the Palettes ( 팔레트 생성팔레트 생성 ))

Function to create a palette for OpenGL

case WM_CREATE:// Store the device contexthDC = GetDC(hWnd); // Select the pixel formatSetDCPixelFormat(hDC); // 팔레트 만들기hPalette = GetOpenGLPalette(hDC);// Create the rendering context and make

it currenthRC = wglCreateContext(hDC);wglMakeCurrent(hDC, hRC);break;



Palette Disposal

// Window is being destroyed, cleanupcase WM_DESTROY:

// Deselect the current rendering context and delete itwglMakeCurrent(hDC,NULL);wglDeleteContext(hRC);if(hPalette != NULL)

DeleteObject(hPalette);// Tell the application to terminate after the window// is gone.PostQuitMessage(0);break;



Windows PalettesWindows PalettesColor Index Mode

Why Use Color Index Mode?Why Use Color Index Mode?

• Palette animation without palette H/W• 팔레트의 원소를 바꾸므로써 , 화면의 색을 변화시킴 .

• Overcome your color choice Limits on the 3-3-2 palette system - Support really smooth shading on an 8-bit display • somewhat faster in 8-bit color modes

• 컬러들이 저장된 배열의 인덱스를 사용해서 특정 색을 지정 .



Windows PalettesWindows PalettesColor Index Mode

Using Color Index ModeUsing Color Index Mode

• void glIndex(GLint c)void glIndex(GLint c)

Disadvantage• limiting color selection (MS 의 경우는 256 개 색만지원 )• does not support some of OpenGL’s other effects

- lighting, shading, fog, anti-aliasing, alpha blending




Index.exe

List 8-6. Index.c 의 GetRedPalette 함수

다양한 명암의 빬간색으로만 구성된 팔레트를 만드는 코드

( 참고 ) Color Index Mode 를 사용하려면 , PIXELFORMATDESCRIPTOR 의 iPixeType 을 PFD_TYPE_COLORINDEX 로 설정하여야 한다 .




List 8-6. Index.c 의 RenderScene 함수

삼각형의 꼭지점은 밝기가 0( 검은색 ) 인 가장 어두운 색으로 설정함 . 나머지 두 꼭지점은 가장 밝은 빨간색(Index 255) 을 사용함 .

부드럽게 Shading 된 삼각형 (3-3-2 팔레트에서는 불가능 )



SummarySummary

• Color, RGB 요소를 사용하여 색 지정 . RGB color cube

• glColor() 의 사용법

• Coloring, Shading, Dithering, Index, Masking

• 3-3-2 팔레트 구성

(8-bit mode 에서 OpenGL 을 사용하는 경우 )



88COLOR AND SHADINGCOLOR AND SHADING

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hallym university gve lab. 1 graphics and virtual environment laboratory 8 color and shading...

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