Mesa 3D 声称通过 osmesa32 支持 32 位浮点颜色通道。问题是,浮点数被量化为 8 位!有没有其他人注意到这一点?以下是我用于测试的简短程序。你会看到我用特定的浮点颜色绘制了一个平面(占据整个视图),然后读取第一个像素的颜色:
#include <stdio.h>
#include <stdlib.h>
#include "GL/osmesa.h"
#include "GL/glut.h"
#define WIDTH 100
#define HEIGHT 100
void draw()
{
GLint r, g, b, a;
glGetIntegerv(GL_RED_BITS, &r);
glGetIntegerv(GL_GREEN_BITS, &g);
glGetIntegerv(GL_BLUE_BITS, &b);
glGetIntegerv(GL_ALPHA_BITS, &a);
printf("channel sizes: %d %d %d %d\n", r, g, b, a);
glEnable(GL_DEPTH_TEST);
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0, 0.0, -1.0);
// draw a plane
glBegin(GL_QUADS);
glColor3f(0.5f, 0.56789f, 0.568f);
glVertex3f(-1, -1, 0);
glVertex3f(-1, 1, 0);
glVertex3f(1, 1, 0);
glVertex3f(1, -1, 0);
glEnd();
glFinish();
}
int main( int argc, char *argv[] )
{
GLfloat *buffer;
/* Create an RGBA-mode context */
#if OSMESA_MAJOR_VERSION * 100 + OSMESA_MINOR_VERSION >= 305
/* specify Z, stencil, accum sizes */
OSMesaContext ctx = OSMesaCreateContextExt( GL_RGB, 16, 0, 0, NULL );
#else
OSMesaContext ctx = OSMesaCreateContext( GL_RGB, NULL );
#endif
if (!ctx) {
printf("OSMesaCreateContext failed!\n");
return 0;
}
/* Allocate the image buffer */
buffer = (GLfloat *) malloc( WIDTH * HEIGHT * 3 * sizeof(GLfloat));
if (!buffer) {
printf("Alloc image buffer failed!\n");
return 0;
}
/* Bind the buffer to the context and make it current */
if (!OSMesaMakeCurrent( ctx, buffer, GL_FLOAT, WIDTH, HEIGHT )) {
printf("OSMesaMakeCurrent failed!\n");
return 0;
}
draw();
printf("RED: %f\n", buffer[0]);
printf("GREEN: %f\n", buffer[1]);
printf("BLUE: %f\n", buffer[2]);
/* free the image buffer */
free( buffer );
/* destroy the context */
OSMesaDestroyContext( ctx );
return 0;
}
在绘图代码中,行:
glColor3f(0.5f, 0.56789f, 0.568f);
应该给我浮动颜色值。当我阅读颜色时,我得到以下输出:
channel sizes: 32 32 32 32
RED: 0.501961
GREEN: 0.568627
BLUE: 0.568627
您会注意到 0.501961 = 128/255,并且 0.568627=145/255(即量化)。
我在我的 Mac 上使用以下配置构建了 Mesa:
./configure --with-driver=osmesa --with-osmesa-bits=32 --disable-gallium --disable-egl