is What an Attribute Primitives and Attributes
September 4, 2002
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An attribute changes the appearance of a primitive.
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Color Line type (dotted, dashed, etc...) Line width filled or unfilled (polygon) italic, bold, or plain (text)
Changing Colors
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Example
glBegin(GL_LINELOOP); for ( angle = 0.0; angle < 2.0 * M_PI; angle += 0.2) { glVertex3f(1.0 * cos(angle), 1.0 * sin(angle), 0.0); glColor3f(angle / 2.0*M_PI, 1.0 angle / 2.0 * M_PI, angle / 2.0 * M_PI); } glEnd();
Setting a color:
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glColor3f( redComponent, greenComponent, blueComponent); all components (for floats and doubles) go from 0.0 to 1.0.
Line Style
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Example -- Stippling
glEnable(GL_LINE_STIPPLE); glLineStipple(1, 0xf00f); glBegin (GL_LINES); glVertex3f(-1.0, 1.0, 0.0); glVertex3f( 1.0, 1.0, 0.0); glEnd(); glLineStipple(1, 0xaaaa); glBegin(GL_LINES); glVertex(-1.0, 0.0, 0.0); glVertex( 1.0, 0.0, 0.0); glEnd;
glLineStipple (
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GLint factor, GLushort pattern); glEnable (GL_LINE_STIPPLE); The factor is a "stretch" factor that will stretch out the pattern. The pattern is the bit pattern to use.
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0x00ff (dashed line) 0xaaaa (dotted line)
Line Width
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Polygon Attributes
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glLineWidth( GLfloat width);
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default width line is 1.0
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Example
for (width = 1.0; width < 4.0; width += 1.0) { glLineWidth(width); glBegin(GL_LINES); glVertex(-1.0, -2.0+width, 0.0); glVertex( 1.0, -2.0+width, 0.0); glEnd(); }
glPolygonMode(GLenum face, GLenum mode); Faces
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GL_FRONT GL_BACK GL_FRONT_AND_BACK GL_POINT GL_LINE GL_FILL
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Modes
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Stippling Polygons
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Example
GLubyte *pattern[128] = {...}; glEnable(GL_POLYGON_STIPPLE); glPolygonStipple(pattern); glBegin(GL_POLYGON); glVertex3f(-1.0, -1.0, 0.0); glVertex3f( 1.0, -1.0, 0.0); glVertex3f( 0.0, 1.0, 0.0); glEnd(); glDisable(GL_POLYGON_STIPPLE);
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You can also stipple polygons but you will use a 2 D array. glPolygonStipple(const GLubyte *mask); You also need to enable or...