[For David] Half Dynamic Range

OneSadCookie

Luminary

Posts: 5,125
Joined: 2002.04

Post: #1

Aug 9, 2003 — 01:24 AM

Here's how to compute (tex - 0.5) * 2 using texture_env_combine.

Executive summary:

Code:

glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);

    GLfloat subtractColor[4] = { 0.5, 0.5, 0.5, 0.0 };

    glTexEnvfv(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COLOR, subtractColor);

    glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_SUBTRACT);

    glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_TEXTURE);

    glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_CONSTANT);

    glTexEnvf(GL_TEXTURE_ENV, GL_RGB_SCALE, 2.0f);

Full working program:

Code:

#include <stdlib.h>

#if defined(__APPLE_CC__)

#include <GLUT/glut.h>

#include <OpenGL/glext.h>

#else

#include <GL/glut.h>

#include <GL/glext.h>

#endif

GLubyte texture[16] =

{

    192, 0, 0, 255,

    0, 192, 0, 255,

    0, 0, 192, 255,

    192, 192, 0, 255

};

void display(void)

{

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    static GLdouble angle = 0.0;

    angle += 0.001;

    if (angle > 6.283185308)

    {

        angle -= 6.283185308;

    }

    glLoadIdentity();

    gluLookAt(5.0, 5.0, 0.0,

              0.0, 0.0, 0.0,

              0.0, 1.0, 0.0);

    glRotatef(180 * angle / 3.141592654, 0, 1, 0);

    glBegin(GL_QUADS);

    glTexCoord2f(0, 0);

    glVertex2f(-1, -1);

    glTexCoord2f(1, 0);

    glVertex2f(1, -1);

    glTexCoord2f(1, 1);

    glVertex2f(1, 1);

    glTexCoord2f(0, 1);

    glVertex2f(-1, 1);

    glEnd();

    glutSwapBuffers();

    glutReportErrors();

}

void reshape(int width, int height)

{

    glViewport(0, 0, width, height);

    glMatrixMode(GL_PROJECTION);

    glLoadIdentity();

    gluPerspective(45.0, (GLdouble)width/(GLdouble)height, 0.01, 100);

    glMatrixMode(GL_MODELVIEW);

}

void idle(void)

{

    glutPostRedisplay();

}

int main(int argc, char** argv)

{

    glutInit(&argc, argv);

    glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH);

    glutInitWindowSize(640, 480);

    (void)glutCreateWindow("GLUT Program");

    glutDisplayFunc(display);

    glutReshapeFunc(reshape);

    glutIdleFunc(idle);

    glEnable(GL_TEXTURE_2D);

    glEnable(GL_CULL_FACE);

    glBindTexture(GL_TEXTURE_2D, 1);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 2, 2, 0,

                 GL_RGBA, GL_UNSIGNED_BYTE, texture);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);

    GLfloat subtractColor[4] = { 0.5, 0.5, 0.5, 0.0 };

    glTexEnvfv(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COLOR, subtractColor);

    glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_SUBTRACT);

    glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_TEXTURE);

    glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_CONSTANT);

    glTexEnvf(GL_TEXTURE_ENV, GL_RGB_SCALE, 2.0f);

    glutMainLoop();

    return EXIT_SUCCESS;

}

inio

Member

Posts: 145
Joined: 2002.06

Post: #2

Aug 9, 2003 — 06:07 PM

Not sure what this is for, but if you're looking for something like Unreal's Modulate mode, you want something like this:

glBlendFunc(GL_DST_COLOR,GL_SRC_COLOR);

Drawing with that blend mode, black will turn what it's drawn on top of black, 50% gray will leave the background unaltered, and white will double the brightness of what it's drawn on top of.

"He who breaks a thing to find out what it is, has left the path of wisdom."
- Gandalf the Gray-Hat
Bring Alistair Cooke's America to DVD!

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