opengl shader problems with mrt - c++

Question

I have two textures with same size attached to one fbo, and I want to render another texture into one of the attached textures, and I want to render a blue shape of the figure of the input texture to the other fbo attached texture.
the (updated) vertex shader:
#version 330
in vec2 coord;
out vec2 f_coord;
void main() {
gl_Position = vec4(coord, 0.0, 1.0);
f_coord = (1.0+coord)/2.0;
}
the (updated) fragment shader:
#version 330
uniform sampler2D my_texture;
in vec2 f_coord;
out vec4 FragData[2];
void main() {
if(texture(my_texture,f_coord).a == 0.0)
discard;
FragData[0]=texture(my_texture,f_coord);
FragData[1]=vec4(0.5, 0.5, 1.0, 1.0);
}
With this fragment shader everything works fine. The texture and the blue stamp of the texture contures are rendered properly.
Here is a screenshot:
http://s14.directupload.net/file/d/3487/kvkqdbl7_png.htm
But if I want to render the texture into gl_FragData[1] and the blue conture stamp into gl_FragData[0]
#version 330
uniform sampler2D my_texture;
in vec2 f_coord;
out vec4 FragData[2];
void main() {
if(texture(my_texture,f_coord).a == 0.0)
discard;
FragData[0]=vec4(0.5, 0.5, 1.0, 1.0);
FragData[1]=texture(my_texture,f_coord);
}
than I get two totally blue textures. The strange thing is: Both target textures are totally blue, but I have set the glViewport just to a part of the texture.
Here a screenshot:
http://s1.directupload.net/file/d/3487/9loqibdc_png.htm
The fbo attachments have the half screen size
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, glutGet(GLUT_WINDOW_WIDTH)/2, glutGet(GLUT_WINDOW_HEIGHT), 0, GL_RGBA, GL_BYTE, 0);
So I can render both textures to the screen for checking.
This is how I created the framebufferobject
void init_fbo()
{
glGenTextures(1, &fbo.texture0);
glBindTexture(GL_TEXTURE_2D, fbo.texture0);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, glutGet(GLUT_WINDOW_WIDTH)/2, glutGet(GLUT_WINDOW_HEIGHT), 0, GL_RGBA, GL_BYTE, 0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glGenTextures(1, &fbo.texture1);
glBindTexture(GL_TEXTURE_2D, fbo.texture1);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, glutGet(GLUT_WINDOW_WIDTH)/2, glutGet(GLUT_WINDOW_HEIGHT), 0, GL_RGBA, GL_BYTE, 0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glBindTexture(GL_TEXTURE_2D, 0);
glGenFramebuffers(1, &fbo.fbo);
glBindFramebuffer(GL_FRAMEBUFFER, fbo.fbo);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
fbo.texture0, 0);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, GL_TEXTURE_2D,
fbo.texture1, 0);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
}
I use those global struct variables
struct
{
GLuint fbo;
GLuint texture0;
GLuint texture1;
} fbo;
struct
{
GLuint program;
GLint uni_texture;
GLint att_coord;
} shader_fbo;
struct
{
GLuint program;
GLint uni_texture;
GLint att_coord;
} shader_screen;
And this is my render function
void render()
{
GLenum buffers[2];
GLfloat vertices[] = { -1.0, -1.0,
-1.0, 1.0,
1.0, -1.0,
1.0, 1.0 };
GLubyte indices[] = { 0, 1, 2,
1, 2, 3 };
/*render to mrt fbo*/
glUseProgram(shader_fbo.program);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texture.texID);
glUniform1i(shader_fbo.uni_texture, 0);
glEnableVertexAttribArray(shader_fbo.att_coord);
glVertexAttribPointer(shader_fbo.att_coord,
2,
GL_FLOAT,
GL_FALSE,
0,
vertices);
glBindFramebuffer(GL_FRAMEBUFFER, fbo.fbo);
buffers[0] = GL_COLOR_ATTACHMENT0;
buffers[1] = GL_COLOR_ATTACHMENT1;
glDrawBuffers(2, buffers);
glViewport(0, 0,
texture.width, texture.height);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texture.texID);
glUniform1i(shader_fbo.uni_texture, 0);
glClear(GL_COLOR_BUFFER_BIT);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_BYTE, indices);
glDisableVertexAttribArray(shader_fbo.att_coord);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
glBindTexture(GL_TEXTURE_2D, 0);
/*render both textures now to screen*/
glUseProgram(shader_screen.program);
glEnableVertexAttribArray(shader_screen.att_coord);
glVertexAttribPointer(shader_screen.att_coord,
2,
GL_FLOAT,
GL_FALSE,
0,
vertices);
/*render the first texture to the left side of the screen*/
glViewport(0, 0,
glutGet(GLUT_WINDOW_WIDTH)/2, glutGet(GLUT_WINDOW_HEIGHT));
glClear(GL_COLOR_BUFFER_BIT);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, fbo.texture0);
glUniform1i(shader_screen.uni_texture, 0);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_BYTE, indices);
/*render the second texture to the right side of the screen*/
glViewport(glutGet(GLUT_WINDOW_WIDTH)/2, 0,
glutGet(GLUT_WINDOW_WIDTH)/2, glutGet(GLUT_WINDOW_HEIGHT));
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, fbo.texture1);
glUniform1i(shader_screen.uni_texture, 0);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_BYTE, indices);
glutSwapBuffers();
}