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POopengl: rendering to texture goes wrong
 

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  1. POopengl: rendering to texture goes wrong
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    <p>I've written a program for testing rendering a texture with the framebuffer. In the function render_texture() I want to render a triangle on to a texture, but when I display the rendered texture in the display function, I get just a simple yellow square.</p> <pre><code>#include "GL/glew.h" #include "GL/glext.h" #include "GL/glu.h" #include "GL/freeglut.h" #include &lt;cstdio&gt; uint16_t tex_width = 75; uint16_t tex_height = 24; GLuint texture; int w1; int h1; void orthogonalStart (int w, int h) { glMatrixMode(GL_PROJECTION); glPushMatrix(); glLoadIdentity(); gluOrtho2D(0, w, 0, h); glScalef(1, -1, 1); glTranslatef(0, -h1, 0); glMatrixMode(GL_MODELVIEW); } void orthogonalEnd (void) { glMatrixMode(GL_PROJECTION); glPopMatrix(); glMatrixMode(GL_MODELVIEW); } void display (void) { glClearColor (0.0,0.0,0.0,1.0); glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); orthogonalStart(w1, h1); glBegin(GL_QUADS); glTexCoord2f(0, 0); glVertex2f(125, 125); glTexCoord2f(0, 1); glVertex2f(125, 125+tex_height); glTexCoord2f(1, 1); glVertex2f(125+tex_width, 125+tex_height); glTexCoord2f(1, 0); glVertex2f(125+tex_width, 125); glEnd(); orthogonalEnd(); glutSwapBuffers(); } void reshape (int w, int h) { glViewport (0, 0, (GLsizei)w, (GLsizei)h); glMatrixMode (GL_PROJECTION); glLoadIdentity (); gluPerspective (60, (GLfloat)w / (GLfloat)h, 0.1, 1000.0); w1 = w; h1 = h; glMatrixMode (GL_MODELVIEW); } void render_texture() { GLuint framebuffer = 0; glGenFramebuffers(1, &amp;framebuffer); glBindFramebuffer(GL_FRAMEBUFFER, framebuffer); glGenTextures(1, &amp;texture); glBindTexture(GL_TEXTURE_2D, texture); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, tex_width, tex_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0); GLenum draw_buffers[1] = {GL_COLOR_ATTACHMENT0}; glDrawBuffers(1, draw_buffers); if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) { fprintf(stderr, "[render_texture] Fehler im Framebuffer\n"); exit(1); } glBindFramebuffer(GL_FRAMEBUFFER, framebuffer); glViewport(0, 0, tex_width, tex_height); glClearColor (0.0,0.0,0.0,1.0); orthogonalStart(tex_width, tex_height); glColor4f(1, 1, 0, 0); glBegin(GL_TRIANGLES); glVertex2f(0.f,0.f); glVertex2f(tex_width, 0.0f); glVertex2f(tex_width, (GLfloat)tex_height/2.f); //glVertex2f(tex_width-(GLfloat)tex_height/2.f, tex_height); //glVertex2f(0, tex_height); glEnd(); orthogonalEnd(); glBindFramebuffer(GL_FRAMEBUFFER, 0); } int main (int argc, char **argv) { glutInit (&amp;argc, argv); glutInitDisplayMode (GLUT_DOUBLE | GLUT_DEPTH | GLUT_RGBA); glutInitWindowSize (500, 500); glutInitWindowPosition (100, 100); glutCreateWindow (""); glutDisplayFunc (display); glutIdleFunc (display); glutReshapeFunc (reshape); glewExperimental=true; GLenum err=glewInit(); if(err!=GLEW_OK) { //Problem: glewInit failed, something is seriously wrong. fprintf(stderr, "glewInit failed, aborting.\n"); } render_texture(); glutMainLoop (); return 0; } </code></pre> <p>Edit 1: I've updated the code, now I have just a blank black screen</p> <pre><code>#include "GL/glew.h" #include "GL/glext.h" #include "GL/glu.h" #include "GL/freeglut.h" #include &lt;cstdio&gt; uint16_t tex_width = 75; uint16_t tex_height = 24; GLuint texture; void orthogonalStart (int w, int h) { glMatrixMode(GL_PROJECTION); glPushMatrix(); glLoadIdentity(); gluOrtho2D(0, w, 0, h); glScalef(1, -1, 1); glTranslatef(0, -glutGet(GLUT_WINDOW_HEIGHT), 0); glMatrixMode(GL_MODELVIEW); } void orthogonalEnd (void) { glMatrixMode(GL_PROJECTION); glPopMatrix(); glMatrixMode(GL_MODELVIEW); } void display (void) { glClearColor (0.0,0.0,0.0,1.0); glClear (GL_COLOR_BUFFER_BIT); glLoadIdentity(); orthogonalStart(glutGet(GLUT_WINDOW_WIDTH), glutGet(GLUT_WINDOW_HEIGHT)); glColor3f(1,1,1); glEnable(GL_TEXTURE_2D); glBindTexture(GL_TEXTURE_2D, texture); glBegin(GL_QUADS); glTexCoord2f(0, 0); glVertex2f(125, 125); glTexCoord2f(0, 1); glVertex2f(125, 125+tex_height); glTexCoord2f(1, 1); glVertex2f(125+tex_width, 125+tex_height); glTexCoord2f(1, 0); glVertex2f(125+tex_width, 125); glEnd(); glDisable(GL_TEXTURE_2D); orthogonalEnd(); glutSwapBuffers(); } void reshape (int w, int h) { glViewport (0, 0, (GLsizei)w, (GLsizei)h); glMatrixMode (GL_PROJECTION); glLoadIdentity (); gluPerspective (60, (GLfloat)w / (GLfloat)h, 0.1, 1000.0); glMatrixMode (GL_MODELVIEW); } void render_texture() { GLuint framebuffer = 0; glGenFramebuffers(1, &amp;framebuffer); glBindFramebuffer(GL_FRAMEBUFFER, framebuffer); glGenTextures(1, &amp;texture); glBindTexture(GL_TEXTURE_2D, texture); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, tex_width, tex_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0); GLenum draw_buffers[1] = {GL_COLOR_ATTACHMENT0}; glDrawBuffers(1, draw_buffers); if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) { fprintf(stderr, "[render_texture] Fehler im Framebuffer\n"); exit(1); } glViewport(0, 0, tex_width, tex_height); glBindFramebuffer(GL_FRAMEBUFFER, framebuffer); orthogonalStart(tex_width, tex_height); glColor4f(1, 1, 0, 0); glBegin(GL_TRIANGLES); glVertex2f(0.f,0.f); glVertex2f(tex_width, 0.0f); glVertex2f(tex_width, (GLfloat)tex_height/2.f); //glVertex2f(tex_width-(GLfloat)tex_height/2.f, tex_height); //glVertex2f(0, tex_height); glEnd(); orthogonalEnd(); glBindFramebuffer(GL_FRAMEBUFFER, 0); } int main (int argc, char **argv) { glutInit (&amp;argc, argv); glutInitContextVersion(3, 1); glutInitContextProfile(GLUT_CORE_PROFILE); glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGBA); glutInitWindowSize (500, 500); glutCreateWindow (""); glutDisplayFunc (display); glutIdleFunc (display); glutReshapeFunc (reshape); glewExperimental=true; GLenum err=glewInit(); if(err!=GLEW_OK) { //Problem: glewInit failed, something is seriously wrong. fprintf(stderr, "glewInit failed, aborting.\n"); } //glEnable(GL_TEXTURE_2D); render_texture(); glutMainLoop (); return 0; } </code></pre>
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    1. PTQuestion
    1. USuser2798943
    1. USuser2798943
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      1. PTAnswer
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    1. COJust my standard suggestion: Move that code from reshape into display, and you can save yourself the trouble of pushing and poping matrices. Use glutGet(GLUT_WINDOW_{WIDTH,HEIGHT}) to get the window size.
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      1. POopengl: rendering to texture goes wrong
      1. USdatenwolf
 

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