Rendering two overlapping 2D objects with 2 shaders - c++

Question

I want to render two triangles in blue and a "windmill" in red. To do this I have created 2 shaders, which are the same except for the color. The two triangles are a lot bigger than the "windmill". The problem I'm facing is that if I switch between shaders, ONLY the last object will be rendered. If I switch to using only 1 shader, both objects will be drawn, but I can barely see the "windmill" because of the same color. So my question is how to draw both objects with two shaders? (I know I can just pass a color to the fragment shader, but I don't want to do that).
Render loop:
GLint index, index2;
index = glGetUniformLocation(shaders[LINE], "projectionMatrix");
index2 = glGetUniformLocation(shaders[TRIANGLE], "projectionMatrix");
glUniformMatrix3fv(index, 1, true, value_ptr(projectionMatrix));
glUniformMatrix3fv(index2, 1, true, value_ptr(projectionMatrix));
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(shaders[TRIANGLE]);
glBindVertexArray(vaos[TRIANGLE]);
glDrawArrays(GL_TRIANGLES, 0, tbufindex/sizeof(glm::vec3));
glUseProgram(shaders[LINE]); // If I comment out this line both objects will be drawn
glBindVertexArray(vaos[LINE]);
glDrawArrays(GL_LINE_STRIP, 0, sizeof(vertices_position)/sizeof(glm::vec3));
Line/Triangle.vert:
#version 450
layout (location = 0) in vec3 vPosition;
uniform mat3 projectionMatrix;
void main()
{
vec3 tmp = projectionMatrix*vPosition;
gl_Position = vec4(tmp, 1.0f);
}
Line/triangle.frag:
#version 450
in vec4 gl_FragCoord;
out vec4 fColor;
void main()
{
fColor = vec4(0.0, 0.0, 1.0, 1.0);
}
Also note that I don't have GL_DEPTH_TEST enabled, I'm using 2D coordinates.
Edit positions:
triangles[2] = { { vec3(-0.90f, -0.90f, 1.0f), vec3(0.85f, -0.90f, 1.0f), vec3(-0.90f, 0.85f, 1.0f) },
{ vec3(0.90f, -0.85f, 1.0f), vec3(0.90f, 0.90f, 1.0f), vec3(-0.85f, 0.90f, 1.0f) } };
lines[39] = {
0.0f, 0.0f, 1.0f,
0.5f, 0.0f, 1.0f,
0.5f, 0.5f, 1.0f,
0.0f, 0.0f, 1.0f,
0.0f, 0.5f, 1.0f,
-0.5f, 0.5f, 1.0f,
0.0f, 0.0f, 1.0f,
-0.5f, 0.0f, 1.0f,
-0.5f, -0.5f, 1.0f,
0.0f, 0.0f, 1.0f,
0.0f, -0.5f, 1.0f,
0.5f, -0.5f, 1.0f,
0.0f, 0.0f, 1.0f
};

Answer 1

glUniform..() must be called after binding the program (source). So the following should work:
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(shaders[TRIANGLE]);
glUniformMatrix3fv(index2, 1, true, value_ptr(projectionMatrix));
glBindVertexArray(vaos[TRIANGLE]);
glDrawArrays(GL_TRIANGLES, 0, tbufindex/sizeof(glm::vec3));
glUseProgram(shaders[LINE]); // If I comment out this line both objects will be drawn
glUniformMatrix3fv(index, 1, true, value_ptr(projectionMatrix));
glBindVertexArray(vaos[LINE]);
glDrawArrays(GL_LINE_STRIP, 0, sizeof(vertices_position)/sizeof(glm::vec3));